ARM: OMAP2+: Try to parse earlycon from parent too

With ti-sysc driver the "ti,hwmods" property will be moved to the
interconnect target module instead of the child device. To keep
earlycon working, we need to match against the interconnect target
module in the ti-sysc case.

Cc: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>