BaseTools/Ecc: Replace deprecated function time.clock()

BaseTools/Ecc: Replace deprecated function time.clock()

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=2707

Ecc fails with Python 3.8 because it uses the deprecated time.clock()
function - https://docs.python.org/3.7/library/time.html#time.clock

This change updates EccMain.py to use time.perf_counter().

Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>