Change in coreboot[master]: device/mmio.h: Move readXp/writeXp helpers to device/mmio.h

[Hung-Te Lin (Code Review)]

Attention is currently required from: Arthur Heymans, Julius Werner, Angel Pons, Jianjun Wang.
Hung-Te Lin has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/62561 )

Change subject: device/mmio.h: Move readXp/writeXp helpers to device/mmio.h
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Patch Set 2:

(1 comment)

File src/arch/x86/include/arch/mmio.h:

https://review.coreboot.org/c/coreboot/+/62561/comment/c290b81d_6fd56065 
PS2, Line 8: static __always_inline uint8_t read8(const volatile void *addr)
           : {
           : 	return *((volatile uint8_t *)(addr));
           : }
> we may also need to move these into the top mmio.h.

sorry, just realized this is actually really arch dependent, and the missing one was only read/write64.

so please ignore my previous comment - we should keep it here.