ARM: OMAP: Clean-up dmtimer reset code

Only OMAP1 devices use the omap_dm_timer_reset() and so require the
omap_dm_timer_wait_for_reset() and __omap_dm_timer_reset() functions.
Therefore combine these into a single function called omap_dm_timer_reset()
and simplify the code.

The omap_dm_timer_reset() function is now the only place that is using the
omap_dm_timer structure member "sys_stat". Therefore, remove this member and
just use the register offset definition to simplify and clean-up the code. The
TISTAT register is only present on revision 1 timers and so check for this in
the omap_dm_timer_reset() function.

Please note that for OMAP1 devices, the TIOCP_CFG register does not have the
clock-activity field and so when we reset the timer for an OMAP1 device we
only need to configure the idle-mode field in the TIOCP_CFG register.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>