dsp: avtimer: Update function pointers for camera isp to use avtimer

After DLKM, avtimer functions cannot be invoked directly
from kernel driver. Camera driver exposes API to get the
function pointers to use avtimer. Update the function
pointers by calling respective camera set API.
AVTIMER_LEGACY config should be enabled in audio conf
to enable this support.

CRs-Fixed: 2201340
Change-Id: I165e7ea0226e174288f3e8b81ef01fce137e2e35
Signed-off-by: Laxminath Kasam <lkasam@codeaurora.org>