arm64: Make ARMV8_DEPRECATED depend on SYSCTL

If CONFIG_SYSCTL=n and CONFIG_ARMV8_DEPRECATED=y, the deprecated
instruction emulation code currently leaks some memory at boot
time, and won't have any runtime control interface.  This does
not feel like useful or intended behaviour...

This patch adds a dependency on CONFIG_SYSCTL, so that such a
kernel can't be built in the first place.

It's probably not worth adding the error-handling / cleanup code
that would be needed to deal with this otherwise: people who
desperately need the emulation can still enable SYSCTL.

Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>