arm64: Factor out fixmap initialization from ioremap

The fixmap API was originally added for arm64 for
early_ioremap purposes. It can be used for other purposes too
so move the initialization from ioremap to somewhere more
generic. This makes it obvious where the fixmap is being set
up and allows for a cleaner implementation of __set_fixmap.

Change-Id: I09307d2b8b1db2bb49739f6bd06006538d121d49
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Git-commit: af86e5974d3069bd26ebcf7c046c6e59726acaaa
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


[rvaswani@codeaurora.org: Resolve merge conflicts]
Signed-off-by: Rohit Vaswani <rvaswani@codeaurora.org>