drivers: iio: imu: Fix cpu latency issue for asm330 irq

CPU is taking 500us to 1ms time to come out of deep state of lpm mode to
serve the irq. Due to latency of asm330 IRQ handler, there is drift
b/w the timestamp of data samples. To avoid this changed cpu state
to idle state with timer till IRQ get served.

Change-Id: I31ba873afaae633327de32853b49cce78e9b81ab
Signed-off-by: Puneet Yatnal <puneet@codeaurora.org>