[PATCH] arm64: Add support for ARMv8.2-LPA (52-bit PA support)

ARMv8.2-LPA architecture extension (if available on underlying hardware)
can support 52-bit physical addresses, while the kernel virtual
addresses remain 48-bit.

Make sure that we read the 52-bit PA address capability from
'MAX_PHYSMEM_BITS' variable (if available in vmcoreinfo) and
accordingly change the pte_to_phy() mask values and also traverse
the page-table walk accordingly.

Also make sure that it works well for the existing 48-bit PA address
platforms and also on environments which use newer kernels with 52-bit
PA support but hardware which is not ARM8.2-LPA compliant.

Kernel commit 1d50e5d0c505 ("crash_core, vmcoreinfo: Append
'MAX_PHYSMEM_BITS' to vmcoreinfo") already supports adding
'MAX_PHYSMEM_BITS' variable to vmcoreinfo.

This patch is in accordance with ARMv8 Architecture Reference Manual

Signed-off-by: Bhupesh Sharma <bhsharma@redhat.com>