ARM: OMAP2+: remove some orphan function declarations.

commit 2fd149645eb (ARM: OMAP2+: UART: Remove omap_uart_can_sleep and
add pm_qos) removed omap_uart_can_sleep and omap3_can_sleep, but not
their declarations.  So remove those now.

Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Shubhrajyoti D <shubhrajyoti@ti.com>
[khilman@ti.com: minor changelog edits]
Signed-off-by: Kevin Hilman <khilman@ti.com>