arm64: vdso32: Remove a bunch of #ifdef CONFIG_COMPAT_VDSO guards

Most of the compat vDSO code can be built and guarded using IS_ENABLED,
so drop the unnecessary #ifdefs.

Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>