ARM64: copy CONFIG_CMDLINE_EXTEND from ARM

Copy the config choice for CONFIG_CMDLINE_EXTEND from
arch/arm/Kconfig, including CONFIG_CMDLINE_FROM_BOOTLOADER
as the default.  These will be used by drivers/of/fdt.c.

Change-Id: I8416038498ddf8fc1e99ab06109825eb1492aa7f
Signed-off-by: Colin Cross <ccross@android.com>
Git-commit: 3c1a22b84e6a8cacc810d8371ee1e8e85d68b878
Git-repo: https://android.googlesource.com/kernel/common.git


Signed-off-by: Ian Maund <imaund@codeaurora.org>