sky2: edge triggered workaround enhancement

Need to make the edge-triggered workaround timer faster to get marginally
better peformance. The test_and_set_bit in schedule_prep() acts as a barrier
already. Make it a module parameter so that laptops who are concerned
about power can set it to 0; and user's stuck with broken BIOS's
can turn the driver into pure polling.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>