arm64: sysreg: Remove unused and rotting SCTLR_ELx field definitions

Our SCTLR_ELx field definitions are somewhat over-engineered in that
they carefully define masks describing the RES0/RES1 bits and then use
these to construct further masks representing bits to be set/cleared for
the _EL1 and _EL2 registers.

However, most of the resulting definitions aren't actually used by
anybody and have subsequently started to bit-rot when new fields have
been added by the architecture, resulting in fields being part of the
RES0 mask despite being defined and used elsewhere.

Rather than fix up these masks, simply remove the unused parts entirely
so that we can drop the maintenance burden. We can always add things
back if we need them in the future.

Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>