arm64: use common reboot infrastructure

Commit 7b6d864b48d9 (reboot: arm: change reboot_mode to use enum
reboot_mode) changed the way reboot is handled on arm, which has a
direct impact on arm64 as we share the reset driver on the VE platform.

The obvious fix is to move arm64 to use the same infrastructure.

Change-Id: I94027fe95d060405819dee93c070cd0845c97e18
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
[catalin.marinas@arm.com: removed reboot_mode = REBOOT_HARD default setting]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Git-commit: ff701306cd49aaff80fb852323b387812bc76491
Git-Repo: git://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/


[abhimany@codeaurora.org: minor fix to allow compilation]
Signed-off-by: Abhimanyu Kapur <abhimany@codeaurora.org>