MLK-18848-1: drm: imx: dcss: do not turn off DTG LINE0/1 interrupts

MLK-18848-1: drm: imx: dcss: do not turn off DTG LINE0/1 interrupts

DTG registers are double bufferred. Hence, enabling LINE0/1 interrupts
in DTG in frame 0 will actually activate them in frame 1. Hence, the
LINE0/1 interrupts (vblank and ctxld kick) will be missed in frame 0.

This patch will permanently activate the LINE0/1 interrupts in DTG and
only mask/unmask them at irq_steer controller level (disable_irq/enable_irq).

While at it, do the same change for DPR completion interrupts. Since, these are
only used for tracing purposes, the change is not supposed to affect
driver functionality in any way.

Signed-off-by: Laurentiu Palcu <laurentiu.palcu@nxp.com>