microblaze: Fix C99/gnu99 compatiblity for inline functions

'extern inline' is not portable across various C standards. To ensure
compatiblity with various standards/compilers change the functions to
static inline. This is a portable construct and serves as a comparable
definition to 'extern inline' from the gnu90 standard.

Additionally remove the function prototypes as they are not required due
to the functions being declared static and functions are correctly
ordered based on dependence.

Signed-off-by: Nathan Rossi <nathan@nathanrossi.com>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Tom Rini <trini@konsulko.com>
Acked-by: Mans Rullgard <mans@mansr.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>