tspp: fix bam irq request preventing sleep

Registering and resetting BAM device upon initialization of tspp
driver requests bam irq resource, which prevents entering sleep.
Instead, BAM device is now initialized only when first needed which
is when the first channel is opened. BAM device is uninitialized
when channel is closed.

Change-Id: I056acea721fae164b91a2a5e3946028b4c2b6df2
Signed-off-by: Gilad Broner <gbroner@codeaurora.org>