Fix 'tautological-constant-compare' error

Fix 'tautological-constant-compare' error

Fixed below 'tautological-constant-compare' error when building the source
code with latest clang compiler <clang version 11.0.0>.

plat/common/plat_psci_common.c:36:2:
error: converting the result of '<<' to a boolean always evaluates
to true [-Werror,-Wtautological-constant-compare]
        PMF_STORE_ENABLE)
        ^
include/lib/pmf/pmf.h:28:29: note: expanded from macro 'PMF_STORE_ENABLE'
PMF_STORE_ENABLE        (1 << 0)

This error is observed beacuse of CASSERT placed in
"PMF_DEFINE_CAPTURE_TIMESTAMP" which do below stuff:
CASSERT(_flags, select_proper_config);
where _flags = PMF_STORE_ENABLE (1 << 0) which always results true.

Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
Change-Id: Ifa82ea202496a23fdf1d27ea1798d1f1b583a021