arm64/crash_core: Export TCR_EL1.T1SZ in vmcoreinfo

TCR_EL1.TxSZ, which controls the VA space size, is configured by a
single kernel image to support either 48-bit or 52-bit VA space.

If the ARMv8.2-LVA optional feature is present and we are running
with a 64KB page size, then it is possible to use 52-bits of address
space for both userspace and kernel addresses. However, any kernel
binary that supports 52-bit must also be able to fall back to 48-bit
at early boot time if the hardware feature is not present.

Since TCR_EL1.T1SZ indicates the size of the memory region addressed by
TTBR1_EL1, export the same in vmcoreinfo. User-space utilities like
makedumpfile and crash-utility need to read this value from vmcoreinfo
for determining if a virtual address lies in the linear map range.

While at it also add documentation for TCR_EL1.T1SZ variable being
added to vmcoreinfo.

It indicates the size offset of the memory region addressed by
TTBR1_EL1.

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