docs: s390/pci: Improve and update PCI documentation

docs: s390/pci: Improve and update PCI documentation

Update the s390 specific PCI documentation to better reflect current
behavior and terms such as the handling of Isolated VFs via commit
25f39d3dcb48 ("s390/pci: Ignore RID for isolated VFs").

Add a descriptions for /sys/firmware/clp/uid_checking which was added
in commit b043a81ce3ee ("s390/pci: Expose firmware provided UID Checking
state in sysfs") but missed documentation.

Similarly add documentation for the fidparm attribute added by commit
99ad39306a62 ("s390/pci: Expose FIDPARM attribute in sysfs") and
add a list of pft values and their names.

Finally improve formatting of the different attribute descriptions by
adding a separating colon.

Reviewed-by: Farhan Ali <alifm@linux.ibm.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Reviewed-by: Gerd Bayer <gbayer@linux.ibm.com>
Link: https://lore.kernel.org/r/20260407-uid_slot-v8-1-15ae4409d2ce@linux.ibm.com
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>