selftests:timers: remove local CLOCKID defines

timers tests defines CLOCKIDs locally. Remove all local CLOCKIDs except
CLOCK_HWSPECIFIC and use defines from time.h header file.

CLOCK_HWSPECIFIC and CLOCK_SGI_CYCLE are the same and CLOCK_SGI_CYCLE
is deprecated,

Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Acked-by: John Stultz <jstultz@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>