arm64: enable FIX_EARLYCON_MEM kconfig

In order to support earlycon on arm64, we need to enable earlycon fixmap
support.

Signed-off-by: Rob Herring <robh@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Git-commit: 92cc15fcb543a8ab9af5682a2011944e6f48fd4c
[joonwoop@codeaurora.org: fixed trivial merge conflict.]
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>