arm64: sysreg: Correct sign definitions for EIESB and DoubleLock

The `ID_AA64MMFR4_EL1.EIESB` field, is an unsigned enumeration, but was
incorrectly defined as a `SignedEnum` when introduced in commit
cfc680bb ("arm64: sysreg: Add layout for ID_AA64MMFR4_EL1"). This is
corrected to `UnsignedEnum`.

Conversely, the `ID_AA64DFR0_EL1.DoubleLock` field, is a signed
enumeration, but was incorrectly defined as an `UnsignedEnum`. This is
corrected to `SignedEnum`, which wasn't correctly set when annotated as
such in commit ad16d4cf ("arm64/sysreg: Initial unsigned annotations
for ID registers").

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