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

[Jianjun Wang (Code Review)]

Attention is currently required from: Hung-Te Lin, Arthur Heymans, Julius Werner, Angel Pons.
Jianjun Wang 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
......................................................................

Patch Set 2:

(1 comment)

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

https://review.coreboot.org/c/coreboot/+/62561/comment/72e460b9_8a448f6a 
PS2, Line 8: static __always_inline uint8_t read8(const volatile void *addr)
           : {
           : 	return *((volatile uint8_t *)(addr));
           : }
> sorry, just realized this is actually really arch dependent, and the missing one was only read/write […]

Seems we need to keep the read64p/write64p in x86/include/arch/mmio.h? Any suggestions?