ANDROID: enable CONFIG_RTC_DRV_TEST on cuttlefish

CMOS RTC device does not work on cuttlefish due to crosvm not
implementing ACPI b/127373130. Add a dummy software RTC driver.

Fixes following tests on cuttlefish:
VtsKernelApiSysfs#testRtcHctosys
VtsKernelLinuxKselftest#rtc_rtctest

Bug: 127373130
Test: above tests
Signed-off-by: Tri Vo <trong@google.com>
Change-Id: I34b69d7808f465add263c5a940d23aa0737dc60f