MIPS: include: Mark __xchg as __always_inline

MIPS: include: Mark __xchg as __always_inline

Commit ac7c3e4ff401 ("compiler: enable CONFIG_OPTIMIZE_INLINING
forcibly") allows compiler to uninline functions marked as 'inline'.
In cace of __xchg this would cause to reference function
__xchg_called_with_bad_pointer, which is an error case
for catching bugs and will not happen for correct code, if
__xchg is inlined.

Signed-off-by: Thomas Bogendoerfer <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Signed-off-by: Paul Burton <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: James Hogan <[email protected]>
Cc: [email protected]
Cc: [email protected]