powerpc/pseries: make max polling consistent for longer H_CALLs

Currently, plpks_confirm_object_flushed() function polls for 5msec in
total instead of 5sec.

Keep max polling time consistent for all the H_CALLs, which take longer
than expected, to be 5sec. Also, make use of fsleep() everywhere to
insert delay.

Reported-by: Nageswara R Sastry <rnsastry@linux.ibm.com>
Fixes: 2454a7af ("powerpc/pseries: define driver for Platform KeyStore")
Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
Tested-by: Nageswara R Sastry <rnsastry@linux.ibm.com>
Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240418031230.170954-1-nayna@linux.ibm.com