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/southbridge/intel/bd82x6x/early_thermal.c

@@ -6,21 +6,6 @@
 #include "cpu/intel/model_206ax/model_206ax.h"
 #include <cpu/x86/msr.h>
 
-static void write8p(uintptr_t addr, uint8_t val)
-{
-	write8((uint8_t *)addr, val);
-}
-
-static void write16p(uintptr_t addr, uint16_t val)
-{
-	write16((uint16_t *)addr, val);
-}
-
-static uint16_t read16p(uintptr_t addr)
-{
-	return read16((uint16_t *)addr);
-}
-
 /* Temporary address for the thermal BAR */
 #define TBARB_TEMP 0x40000000