Fix compile error for Mbed TF-M V8M target (2)

[ccli8]

[x] I confirm this contribution is my own and I agree to license it with Apache 2.0.
[x] I confirm the moderators may change the PR before merging it in.
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Summary of changes

Continuing #88, this PR tries to fix more compile error for Mbed TF-M V8M target, usually without FLASHIAP. In arm_uc_config.h:

1. Use DEVICE_FLASH as prerequisite to enable ARM_UC_FEATURE_PAL_FLASHIAP
2. Use ARM_UC_FEATURE_PAL_FLASHIAP as prerequisite to enable ARM_UC_FEATURE_PAL_FILESYSTEM

@marcuschangarm

[marcuschangarm]

@ccli8 Thank you! I'll take a look!

[marcuschangarm]

@ccli8 I think it would be better to add a new section for PSA, once it is ready, so that is looks like the other configurations. For example:

#elif defined(UPDATE_CLIENT_STORAGE_PSA)
#define ARM_UC_FEATURE_PAL_FLASHIAP 0
#define ARM_UC_FEATURE_PAL_FLASHIAP_MCUBOOT 0
#define ARM_UC_FEATURE_PAL_BLOCKDEVICE 0
#define ARM_UC_FEATURE_PAL_FILESYSTEM 0
#define ARM_UC_FEATURE_PAL_LINUX 0
#define ARM_UC_FEATURE_PAL_RTL8195AM 0
#define ARM_UC_FEATURE_PAL_PSA 1

You could then name your implementation UPDATE_CLIENT_STORAGE_PSA and hide the code behind the define ARM_UC_FEATURE_PAL_PSA .

[ccli8]

With above modification, this PR is replaced with #92.

[marcuschangarm]

@ccli8 sounds good, lets close this PR and continue the conversation in the other one.

[ccli8]

Close because #92 will cover this one