Fix creating the early arm64 level 2 blocks

In 48ba9b2669e6 we switched from creating level 1 blocks to smaller
level 2 blocks when creating the early arm64 page tables. On issue
was that they had a different meaning for register x7. The former used
it to hold page table attributes, while the latter held just the memory
type. This caused these attributes to be incorrectly shifted.

Fix this by changing the meaning of x7 to hold the block attributes
and fix the only caller that used the old meaning.

Most hardware seems to have handled the bits being off however qemu
failed to boot as reserved bits that should be zero were being set and
qemu fails to clear these when translating from a virtual address to a
physical address.

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