unified: merge NANO_TIMERS and NANO_TIMEOUTS with SYS_CLOCK_EXISTS

Timers are based off timeouts now, which can only be enabled when the
system clock is enabled. So the three are really just one setting now.

Keep the NANO_TIMERS and NANO_TIMEOUTS around for now until all
middleware that rely on them is updated. They are always enabled when
SYS_CLOCK_EXISTS is enabled.

Change-Id: Iaef1302ef9ad8fc5640542ab6d7304d67aafcfdc
Signed-off-by: Benjamin Walsh <benjamin.walsh@windriver.com>
9 files changed