arm64: Rename page table BSS section to .bss..pgtbl

arm64: Rename page table BSS section to .bss..pgtbl

Rename the .pgdir.bss section to .bss..pgtbl so that the compiler will
notice the leading ".bss" and mark it as NOBITS by default (rather than
PROGBITS, which would take up space in Image binary, forcing all of the
preceding BSS to be emitted into the image as well). This supersedes the
NOLOAD linker directive, which achieves the same thing, and can be
therefore be dropped.

Also, rename .pgdir to .pgtbl to be more generic, as page tables of
various levels will reside here.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Tested-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>