arm64: head: pass ID map root table address to __enable_mmu()

We will be adding an initial ID map that covers the entire kernel image,
so we will pass the actual ID map root table to use to __enable_mmu(),
rather than hard code it.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20220624150651.1358849-10-ardb@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>