ARM: make get_current() and __my_cpu_offset() __always_inline

The get_current() and __my_cpu_offset() accessors evaluate to only a
single instruction emitted inline, but due to the size of the asm string
that is created for SMP+v6 configurations, the compiler assumes
otherwise, and may emit the functions out of line instead.

So use __always_inline to avoid this.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>