[L] Change in flashrom[main]: rpmc: add rpmc commands feature

[Peter Marheine (Code Review)]

Attention is currently required from: Anastasia Klimchuk, Matti Finder.

Peter Marheine has posted comments on this change by Matti Finder. ( https://review.coreboot.org/c/flashrom/+/84934?usp=email )

Change subject: rpmc: add rpmc commands feature
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Patch Set 1:

(2 comments)

File meson.build:

https://review.coreboot.org/c/flashrom/+/84934/comment/6fb0d9a0_4affdf5c?usp... :
PS1, Line 177: enabled
`enabled` is only true if the feature is set to `enabled` (not `auto`). You probably want `get_option('rpmc').allowed()` since that's true if it's either `auto` or `enabled`.

File rpmc.c:

https://review.coreboot.org/c/flashrom/+/84934/comment/7534816b_ddc98ec5?usp... :
PS1, Line 287: 	unsigned char msg[RPMC_UPDATE_HMAC_KEY_MSG_LENGTH];
I'd prefer to use initializers for arrays like this (throughout this file), to make it less prone to length-related errors.

```
unsigned char msg[RPMC_UPDATE_HMAC_KEY_MSG_LENGTH] = {
  flash->chip->rpmc_ctx.op1_opcode,
  0x01,
  counter_address,
  ...
};
```