When PRI queue occurs overflow, driver should update the OVACKFLG to
the PRIQ consumer register, otherwise subsequent PRI requests will not
be processed.

Cc: Will Deacon <will.deacon@arm.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: NMiao Zhong <zhongmiao@hisilicon.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>