ahci_xgene: Implement the workaround to fix the missing of the edge interrupt...

ahci_xgene: Implement the workaround to fix the missing of the edge interrupt for the HOST_IRQ_STAT.

Due to H/W errata, the HOST_IRQ_STAT register misses the edge interrupt
when clearing the HOST_IRQ_STAT register and hardware reporting the
PORT_IRQ_STAT register happens to be at the same clock cycle.

Signed-off-by: Suman Tripathi <stripathi@apm.com>
Signed-off-by: Tejun Heo <tj@kernel.org>