[S] Change in coreboot[main]: drivers/spi: Stop using a variable-length array, 2nd try

[Julius Werner (Code Review)]

Attention is currently required from: Angel Pons, Arthur Heymans, Elyes Haouas, Felix Held, Nico Huber.

Julius Werner has posted comments on this change by Arthur Heymans. ( https://review.coreboot.org/c/coreboot/+/84059?usp=email )

Change subject: drivers/spi: Stop using a variable-length array, 2nd try
......................................................................

Patch Set 6:

(2 comments)

File src/drivers/spi/spi_flash.c:

https://review.coreboot.org/c/coreboot/+/84059/comment/141b6caf_29192240?usp... :
PS1, Line 317: 		chunk_len = MIN(MAX_FLASH_CMD_DATA_SIZE, chunk_len);
> > Why is this line still necessary when we've already checked that no page_size can be larger than 2 […]

Sorry, not quite sure I understand the problem. What I'm suggesting is a macro like
```
#define DECLARE_SPI_FLASH_VENDOR_INFO(_name, _initializers) \
  const struct spi_flash_vendor_info _name = { _initializers }; \
  _Static_assert(1 << _name.page_size_shift <= MAX_FLASH_CMD_DATA_SIZE, \
    "SPI flash vendor " #_name " uses a flash size that is too large, increase MAX_FLASH_CMD_DATA_SIZE!");
```
which would be used like this
```
DECLARE_SPI_FLASH_VENDOR_INFO(spi_flash_winbond_vi,
  .id = VENDOR_ID_WINBOND,
  .page_size_shift = 8,
  ...
)
```
I think(?) that should work, and we just need to enforce through review that everyone defining such a struct actually uses it.

File src/drivers/spi/spi_flash.c:

https://review.coreboot.org/c/coreboot/+/84059/comment/8f66d14f_2743af6b?usp... :
PS6, Line 141: #endif
This should probably go in stddef.h or some other catchall header (like wherever we used to keep MAYBE_STATIC)?