ARM: OMAP: partial LED fixes

Partial fix for CONFIG_LEDS breakage ... at least allow platforms
using the debug-leds support (H4 for now) to build with the generic
LED support, and default the LED that would be the timer LED to
trigger using the "heartbeat" (timer driven, rate depends on load).

Right now only H2 and P2 seem to have working LED support; this
at least makes H4 less broken.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>