bus: ti-sysc: Detect uarts also on omap34xx

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: Keerthy <j-keerthy@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>