ARM:asm:io.h use static inline

ARM:asm:io.h use static inline

When compiling u-boot with W=1 the extern inline void for
read* is likely causing the most noise. gcc / clang will
warn there is never a actual declaration for these functions.
Instead of declaring these extern make them static inline so
it is actually declared.

Change-Id: Ic42b514a030de64b3f12a4ed427f3ffc71f60ef8
cc: Albert ARIBAUD <albert.u.boot@aribaud.net>
Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>
Signed-off-by: Jae-young Hwang <j-zero.hwang@samsung.com>