arm64: Fix for the arm64 kern_addr_valid() function

arm64: Fix for the arm64 kern_addr_valid() function

Fix for the arm64 kern_addr_valid() function to recognize
virtual addresses in the kernel logical memory map.  The
function fails as written because it does not check whether
the addresses in that region are mapped at the pmd level to
2MB or 512MB pages, continues the page table walk to the
pte level, and issues a garbage value to pfn_valid().

Tested on 4K-page and 64K-page kernels.

Signed-off-by: Dave Anderson <anderson@redhat.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
(cherry picked from commit da6e4cb67c6dd1f72257c0a4a97c26dc4e80d3a7)
Signed-off-by: Mark Brown <broonie@linaro.org>