this change add CONFIG_HAVE_ARCH_BITREVERSE config option,
so that we can use some architecture's bitrev hardware instruction
to do bitrev operation.

Introduce __constant_bitrev* macro for constant bitrev operation.

Change __bitrev16() __bitrev32() to be inline function,
don't need export symbol for these tiny functions.
Signed-off-by: Yalin Wang <yalin.wang@sonymobile.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>