Documentation/arm64: HugeTLB page implementation

Arm v8 architecture supports multiple page sizes - 4k, 16k and
64k. Based on the active page size, the Linux port supports
corresponding hugepage sizes at PMD and PUD(4k only) levels.

In addition, the architecture also supports caching larger sized
ranges (composed of multiple entries) at the PTE and PMD level in the
TLBs using the contiguous bit. The Linux port makes use of this
architectural support to enable additional hugepage sizes.

Describe the two different types of hugepages supported by the arm64
kernel and the hugepage sizes enabled by each.

Acked-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>