Improve error messages from clock_if.m method failures.

Print error message in verbose mode when CLOCK_SETTIME() clock_if.m
method failed. For EFIRT RTC clock, add error code for the failure of
CLOCK_GETTIME() report.

Reviewed by: kevans
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Approved by: re (rgrimes)
Differential revision: https://reviews.freebsd.org/D16972