vdso: support more flags for clock_gettime() vdso interface
vdso: support more flags for clock_gettime() vdso interface

Current vdso(implemented by sentry, and used by the real application)
is a partial implimentation. More specifically, the clock_gettime()
vdso interface only works for CLOCK_REALTIME, CLOCK_BOOTTIME, and
CLOCK_MONOTONIC.

So we support more flags for clock_gettime() vdso interface here, like
CLOCK_REALTIME_COARSE, CLOCK_MONOTONIC_RAW, and CLOCK_MONOTONIC_COARSE,
to accelerate clock_gettime() call of real application.

And their implementations refer to the internal syscall of gvisor.
See function getClock() in pkg/sentry/syscalls/linux/sys_time.go.

Signed-off-by: Chen Hui <466a53bed58a03fb51f2feaf73d9f517efe60e47@tencent.com>

google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor