Improve address generation in the early arm64 boot

The adr instruction allows for an address of +-1M from the instruction.
If we replace these with an adrp and an add instruction we can generate
an address +-4G. The adrp will get an address of the 4k page the label
is within, and the add uses the :lo12: prefix to add just the low bits
to this address.

This will allow us to move things around with fewer issues than if we
needed to keep them within the +-1MB range.

Sponsored by: Innovate UK