arm: add early_ioremap support

This patch uses the generic early_ioremap code to implement
early_ioremap for ARM. The ARM-specific bits come mostly from
an earlier patch from Leif Lindholm <leif.lindholm@linaro.org>
here :

	 https://lkml.org/lkml/2013/10/3/279



Change-Id: I523875442caa8ecf61cc170ed3b72a612ac93427
Signed-off-by: Mark Salter <msalter@redhat.com>
Tested-by: Leif Lindholm <leif.lindholm@linaro.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
[robh: minor re-work in prep for permanent mappings. Fix bug in page
table allocation size. Rework CONFIG_MMU dependency.]
Signed-off-by: Rob Herring <robh@kernel.org>
Git-commit: 24293625537e095c2d5bcc5a63dd23dfaf062ffc
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/robh/linux.git


[vabbar@codeaurora.org: Fixed trivial merge conflicts]
Signed-off-by: Venkatesh Yadav Abbarapu <vabbar@codeaurora.org>