OMAP3: PM: CPUidle: check activity for C2, C3, correct accounting

Use the activity check for states C2 and C3 as well.  This is
primarily to prevent deeper states during UART activity.

Also, if a different state is chosen than the target state, update the
'last_state' accordingly so that CPUidle state accounting is coorect.

Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>