arm64/sve: Fix warnings when SVE is disabled

arm64/sve: Fix warnings when SVE is disabled

In configurations where SVE is disabled we define but never reference the
functions for retrieving the default vector length, causing warnings. Fix
this by move the ifdef up, marking get_default_vl() inline since it is
referenced from code guarded by an IS_ENABLED() check, and do the same for
the other accessors for consistency.

Reported-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20211022141635.2360415-3-broonie@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>