gpio: change inline functions to static inline

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: Ifd835bf0e667afb1cbf2e76bb490664af87c382d
Signed-off-by: Daniel Leung <daniel.leung@intel.com>
1 file changed