xen/arm: Rename SCTLR_* defines and remove unused one

xen/arm: Rename SCTLR_* defines and remove unused one

The SCTLR_* are currently used for SCTLR/HSCTLR (arm32) and
SCTLR_EL1/SCTLR_EL2 (arm64).

The naming scheme is actually quite confusing because they may only be
defined for an archicture (or even an exception level). So it is not easy
for the developer to know which one to use.

The naming scheme is reworked by adding Axx_ELx in each define:
    * xx is replaced by 32 or 64 if specific to an architecture
    * x is replaced by 2 (hypervisor) or 1 (kernel) if specific to an
    exception level

While doing the renaming, remove the unused defines (or at least the ones
that are unlikely going to be used).

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Andrii Anisov <andrii_anisov@epam.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>