arm64: fix missing asm/alternative.h include in kernel/module.c

On next-20150105, defconfig compilation breaks with:

arch/arm64/kernel/module.c:408:4: error: implicit declaration of function ‘apply_alternatives’ [-Werror=implicit-function-declaration]

Fix by including asm/alternative.h, where the apply_alternatives()
prototype is declared.

This second version incorporates a comment from Mark Rutland
<mark.rutland@arm.com> to keep the includes in alphabetical order
by filename.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Paul Walmsley <pwalmsley@nvidia.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>