arch/x86: Provide readXp/writeXp helpers in arch/mmio.h

These p-suffixed helpers allow dropping pointer casts in call-sites,
which is particularly useful when accessing registers at an offset from
a base address. Move existing helpers in chipset code to arch/mmio.h and
create the rest accordingly.

Change-Id: I36a015456f7b0af1f1bf2fdff9e1ccd1e3b11747
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/51862
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Patrick Rudolph <siro@das-labor.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/northbridge/intel/ironlake/raminit.c

@@ -115,16 +115,6 @@ static u16 read_1d0(u16 addr, int split)
 	return val;
 }
 
-static void write32p(uintptr_t addr, uint32_t val)
-{
-	write32((void *)addr, val);
-}
-
-static uint32_t read32p(uintptr_t addr)
-{
-	return read32((void *)addr);
-}
-
 static void sfence(void)
 {
 	asm volatile ("sfence");