Added external spi flash driver.

[itarze]

Added external spi flash driver.

Description

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[itarze]

@tzarc Describe where the document should be added?

[drashna]

presumably: https://github.com/qmk/qmk_firmware/blob/develop/docs/eeprom_driver.md

[tzarc]

Almost, will need a flash_driver.md with descriptions of configurable items, as well as a link to the new page in the sidebar.

[drashna]

Almost, will need a flash_driver.md with descriptions of configurable items, as well as a link to the new page in the sidebar.

I should read more. But should be set up somewhat similarly, I think. At least in the sidebar for the docs, and such.

[tzarc]

As far as I can tell, all the "Kbyte" values have been converted to "byte", please confirm with hardware.

[tzarc]

Please also confirm that usages of uintptr_t have been changed to uint32_t.