s390/pai_crypto: Rename paicrypt_getctr() to pai_getctr()

s390/pai_crypto: Rename paicrypt_getctr() to pai_getctr()

To support one common PAI PMU device driver which handles
both PMUs pai_crypto and pai_ext, use a common naming scheme
for structures and variables suitable for both device drivers.

Rename paicrypt_getctr() to pai_getctr() to reflect is common
purpose. pai_getctr() now uses pai_pmu table to extract PAI PMU
characteristics such as kernel_offset inside the counter area page.
Also rename paicrypt_have_sample() to pai_have_sample().

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Reviewed-by: Jan Polensky <japo@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>