Improve Power Management in SMC911X driver.

device is already in *normal* (D0) mode => it doesn't need to be wake-up.

With this patch, we only wake-up (writing on TEST_BYTE register) if PM_MODE
bits of PM_CTRL register is in sleep (D1/D2) mode.

Signed-off-by: Bertrand Cachet <bertrand.cachet@heig-vd.ch>