arm64: head: factor out TTBR1 assignment into a macro

Create a macro load_ttbr1 to avoid having to repeat the same instruction
sequence 3 times in a subsequent patch. No functional change intended.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20220624150651.1358849-17-ardb@kernel.org


Signed-off-by: Will Deacon <will@kernel.org>