arm64: mm: Reserve enough pages for the initial ID map

The logic that conditionally allocates one additional page at each
swapper page table level if KASLR is enabled is also applied to the
initial ID map, now that we have started using the same set of macros
to allocate the space for it.

However, the placement of the kernel in physical memory might result in
additional pages being needed at any level, even if KASLR is disabled in
the build. So account for this in the computation.

Fixes: c3cee924

 ("arm64: head: cover entire kernel image in initial ID map")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20220826164800.2059148-1-ardb@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>