arm64: pgtable: Decouple PGDIR size macros from PGD/PUD/PMD levels

arm64: pgtable: Decouple PGDIR size macros from PGD/PUD/PMD levels

The mapping from PGD/PUD/PMD to levels and shifts is very confusing,
given that, due to folding, the shifts may be equal for different
levels, if the macros are even #define'd to begin with.

In a subsequent patch, we will modify the ID mapping code to decouple
the number of levels from the kernel's view of how these types are
folded, so prepare for this by reformulating the macros without the use
of these types.

Instead, use SWAPPER_BLOCK_SHIFT as the base quantity, and derive it
from either PAGE_SHIFT or PMD_SHIFT, which -if defined at all- are
defined unambiguously for a given page size, regardless of the number of
configured levels.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20240214122845.2033971-65-ardb+git@google.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>