vm_phys_early_alloc(): Align to PAGE_SIZE; Review callers' alignment

[olce]

Summary

Switch alignment of vm_phys_early_alloc() to PAGE_SIZE as it is the most
used one.

Review all calling points and change those where greater alignment is
really needed to use vm_phys_early_alloc_ex().

In particular, in PowerPC's moea64_page_array_startup(), reduce the
requested alignment to what the hardware actually requires
('moea64_large_page_size') instead of the size of the page array portion
for a full domain.

[olce]

Explicitly mention the change in moea64_page_array_startup() in the commit message.

Impacts of vm_phys_early_alloc_ex()'s change of signature.

Fix a small typo "bug" in mmu_radix_page_array_startup() (a 0 instead of a -1
for the domain value; however, this code is under #ifdef notyet, so not
active).