s390/crc32: Remove have_vxrs static key

s390/crc32: Remove have_vxrs static key

Replace the have_vxrs static key with a cpu_has_vx() call.  cpu_has_vx()
resolves into a compile time constant (true) if the kernel is compiled
for z13 or newer.  Otherwise it generates an unconditional one
instruction branch, which is patched based on CPU alternatives.

In any case the generated code is at least as good as before and avoids
static key handling.

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Link: https://lore.kernel.org/r/20250417125318.12521F12-hca@linux.ibm.com/
Signed-off-by: Eric Biggers <ebiggers@google.com>