accel/ivpu/40xx: Fix buttress interrupt handling

Buttress spec requires that the interrupt status is cleared at
the source first (before clearing MTL_BUTTRESS_INTERRUPT_STAT),
that implies that we have to mask out the global interrupt while
handling buttress interrupts.

Fixes: 79cdc56c

 ("accel/ivpu: Add initial support for VPU 4")
Signed-off-by: Karol Wachowski <karol.wachowski@linux.intel.com>
Signed-off-by: Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>
Reviewed-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230822095238.3722815-1-stanislaw.gruszka@linux.intel.com