arm64: ioremap: add ioremap_cache macro

Add ioremap_cache macro, because some code will test if this macro
is defined or not, and will generate a generric version if not defined,
for example, memremap.c do like this.

Signed-off-by: yalin wang <yalin.wang2010@gmail.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>