arm64: head: Switch endianness before populating the ID map

Ensure that the endianness used for populating the ID map matches the
endianness that the running kernel will be using, as this is no longer
guaranteed now that create_idmap() is invoked before init_kernel_el().

Note that doing so is only safe if the MMU is off, as switching the
endianness with the MMU on results in the active ID map to become
invalid. So also clear the M bit when toggling the EE bit in SCTLR, and
mark the MMU as disabled at boot.

Note that the same issue has resulted in preserve_boot_args() recording
the contents of registers X0 ... X3 in the wrong byte order, although
this is arguably a very minor concern.

Fixes: 32b135a7 ("arm64: head: avoid cache invalidation when entering with the MMU on")
Reported-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20230125185910.962733-1-ardb@kernel.org


Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>