arm64: KGDB: Add Basic KGDB support

arm64: KGDB: Add Basic KGDB support

Add KGDB debug support for kernel debugging.
With this patch, basic KGDB debugging is possible.GDB register
layout is updated and GDB tool can establish connection with
target and can set/clear breakpoints.

Signed-off-by: Vijaya Kumar K <Vijaya.Kumar@caviumnetworks.com>
Reviewed-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
(cherry picked from commit bcf5763b0d58d20e288ac52f96cbd7788e262cac)
Signed-off-by: Mark Brown <broonie@linaro.org>
Conflicts:
	arch/arm64/kernel/Makefile