arm64: mmu: drop paging_init comments

The comments could not reflect the code, and it is easy to get
what this function does from a straight-line reading of the code.
So let's drop the comments

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>