arm64: Define Cortex-A73 MIDR

As we're about to introduce a new workaround that is specific to
Cortex-A73, let's define the coresponding MIDR.

Change-Id: Iabb0e83a0eadddbde458fdafd1224e442b6f3e63
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Git-commit: 199fd2bff4040985fbd7853cc39b7245fcf54bb9
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


[sramana@codeaurora.org: Resolve trivial merge conflicts]
Signed-off-by: Srinivas Ramana <sramana@codeaurora.org>