ARM: OMAP2xxx: PM: fix OMAP2xxx-specific UART idle bug in v3.3

On OMAP2420-based systems, the PM code ignores the state of the UART
functional clocks when determining what idle state to enter.  This
breaks the serial port now that the UART driver's clock behavior can
be controlled via the PM autosuspend timeout.

To fix, remove the special-case idle handling for the UARTs in the
OMAP2420/2430 PM idle code added by commit
4af4016c ("OMAP3: PM: UART: disable
clocks when idle and off-mode support").

Tested on Nokia N800.  This patch is a collaboration between Tony
Lindgren <tony@atomide.com> and Paul Walmsley <paul@pwsan.com>.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Acked-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>