linker: add custom align size to reduce alignment memory wasting

[wentongwu]

1) When enable CONFIG_CUSTOM_SECTION_ALIGN, it need less alignment memory
for image rom region. But it will consume one more MPU region. For example somehow
we can know the size of .text and .rodata section, 512k+4B, with current code and
CONFIG_MPU_REQUIRES_POWER_OF_TWO_ALIGNMENT enabled, the size of .text
and .rodata section in RAM (suppose only RAM) will be 1M.
But if with CONFIG_CUSTOM_SECTION_ALIGN(for example 64k), the size of .text and 
.rodata section will be 512k+64k(MPU_SUB_REGION_SIZE), that saved memory. 
For MPU configuration, 512k will be in MPU region1 and 64k will be in MPU region 2,
it will waste one more MPU region. 
The trade off for enable CONFIG_CUSTOM_SECTION_ALIGN or not should be decided by
end users according their applications, but Zephyr should provide this option.

2) Add custom align size for code relocation to reduce alignment memory wasting.

Fixes: #17337

Signed-off-by: Wentong Wu wentong.wu@intel.com

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[wentongwu]

@ioannisg @andrewboie could you please give some comments about this PR? Thanks

[andrewboie]

when enable CONFIG_CUSTOM_SECTION_ALIGN, it need less alignment
memory for image rom region. But it will consume one more MPU
region. The trade off for enable CONFIG_CUSTOM_SECTION_ALIGN or
not should be decided by end users according their applications,
but Zephyr should provide this option.

I don't understand what you mean by this.
How would section alignment cause an additional MPU region to be used? Please elaborate.

[wentongwu]

when enable CONFIG_CUSTOM_SECTION_ALIGN, it need less alignment
memory for image rom region. But it will consume one more MPU
region. The trade off for enable CONFIG_CUSTOM_SECTION_ALIGN or
not should be decided by end users according their applications,
but Zephyr should provide this option.

I don't understand what you mean by this.
How would section alignment cause an additional MPU region to be used? Please elaborate.

@andrewboie sorry for the confuse, I have updated the comments, please take a look. Thanks

[nashif]

rebase

[backporting]

The backport to v1.14-branch failed:

Commits ["de7aa87e23e8ae92c720f97fc27e6a52b2e42d1a","de7f4d30e886c1f3ac15f137c5cd01d59a2f0f4a"] could not be cherry-picked on top of v1.14-branch

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub.
git fetch
# Create new working tree.
git worktree add .worktrees/backport v1.14-branch
# Navigate to the new directory.
cd .worktrees/backport
# Cherry-pick all the commits of this pull request and resolve the likely conflicts.
git cherry-pick de7aa87e23e8ae92c720f97fc27e6a52b2e42d1a de7f4d30e886c1f3ac15f137c5cd01d59a2f0f4a
# Create a new branch with these backported commits.
git checkout -b backport-17390-to-v1.14-branch
# Push it to GitHub.
git push --set-upstream origin backport-17390-to-v1.14-branch
# Go back to the original working tree.
cd ../..
# Delete the working tree.
git worktree remove .worktrees/backport

Then, create a pull request where the base branch is v1.14-branch and the compare/head branch is backport-17390-to-v1.14-branch.