drm/radeon: Add init interrupt kfd->kgd interface

This patch adds a new interface function to the kfd->kgd interface.
The function is kgd_init_interrupts() and its function is to
initialize a pipe's interrupts.

The function currently enables the timestamp interrupt and the
bad opcode interrupt.

Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>