When compiling with optimization level 0 (-O0), the linker complains
about missing references to uart functions. This is due to compiler
treating this functions as extern, since -O0 disables function inlining,
as described in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49653
So change the declaration to static inline.
Change-Id: I59607cffbd1cae141a9eeaca699549ebf8203061
Signed-off-by: Daniel Leung <daniel.leung@intel.com>