arm64: module: move find_section to header

Move it to the header so that the implementation can be shared
by the alternatives code.

Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Cc: Will Deacon <will@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20220830104833.34636-2-joey.gouly@arm.com


Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>