s390/pkey: pkey cleanup: narrow in-kernel API, fix some variable types

s390/pkey: pkey cleanup: narrow in-kernel API, fix some variable types

There are a lot of pkey functions exported as in-kernel callable
API functions but not used at all. This patch narrows down the
pkey in-kernel API to what is currently only used and exploited.

Within the kernel just use u32 without any leading __u32. Also
functions declared in a header file in arch/s390/include/asm
don't need a comment 'In-kernel API', this is by definition,
otherwise the header file would be in arch/s390/include/uapi/asm.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Reviewed-by: Ingo Franzki <ifranzki@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>