Looks like we currently only detect UART on omap36xx, let's also
add support for omap34xx. And let's also fix the SWSUP mode, it should
be SWSUP_SIDLE for omap3, not SWSUP_SIDLE_ACT like for omap4 and later.

Note that we are still booting omap3 for most part without ti-sysc,
so no need to treat this change as a fix.
Tested-by: NKeerthy <j-keerthy@ti.com>
Signed-off-by: NTony Lindgren <tony@atomide.com>