drm: mali-dp: Enable Global SE interrupts mask for DP500

In the situation that DE and SE aren’t shared the same interrupt number,
the Global SE interrupts mask bit MASK_IRQ_EN in MASKIRQ must be set, or
else other mask bits will not work and no SE interrupt will occur. This
patch enables MASK_IRQ_EN for SE to fix this problem.

Signed-off-by: Alison Wang <alison.wang@nxp.com>
Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>