arm64: hibernate: preserve kdump image around hibernation

Since arch_kexec_protect_crashkres() removes a mapping for crash dump
kernel image, the loaded data won't be preserved around hibernation.

In this patch, helper functions, crash_prepare_suspend()/
crash_post_resume(), are additionally called before/after hibernation so
that the relevant memory segments will be mapped again and preserved just
as the others are.

In addition, to minimize the size of hibernation image, crash_is_nosave()
is added to pfn_is_nosave() in order to recognize only the pages that hold
loaded crash dump kernel image as saveable. Hibernation excludes any pages
that are marked as Reserved and yet "nosave."

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: James Morse <james.morse@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>