hwaccess: replace macros by C code

Split the code for endian conversion into separate files for big and
little endian. The buildsystem selects the correct file for the used
endianness. Replace the swab macros with `static inline` c functions.
Define macros for returning the same or swapped value. Call those macros
in the endian specific files.

Change-Id: I86d38d816b37c283279c485fac8027f8fb94364a
Signed-off-by: Thomas Heijligen <thomas.heijligen@secunet.com>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/62898
Original-Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/72315
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/hwaccess_x86_msr.c b/hwaccess_x86_msr.c
index 79cf2f8..3728061 100644
--- a/hwaccess_x86_msr.c
+++ b/hwaccess_x86_msr.c
@@ -17,7 +17,7 @@
  */
 
 /* MSR abstraction implementations for Linux, OpenBSD, FreeBSD/Dragonfly, OSX, libpayload
- * and a non-working default implementation on the bottom. See also hwaccess.h for some (re)declarations.
+ * and a non-working default implementation on the bottom.
  */
 
 #include "hwaccess_x86_msr.h"