caif-hsi: Make inactivity timeout configurable.

CAIF HSI uses a timer for inactivity. Upon timeout HSI-wake signaling
is initiated to allow power-down of the HSI block.

Signed-off-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>