PCI: aardvark: Use ISR1 instead of ISR0 interrupt in legacy irq mode

The Aardvark has two interrupts sets:

 - first set is bit[23:16] of PCIe ISR 0 register(RD0074840h)

 - second set is bit[11:8] of PCIe ISR 1 register(RD0074848h)

Only one set should be used, while another set should be masked.

The second set, ISR1, is more advanced, the Legacy INT_X status bit is
asserted once Assert_INTX message is received, and de-asserted after
Deassert_INTX message is received which matches what the driver is
currently doing in the ->irq_mask() and ->irq_unmask() functions.

The ISR0 requires additional work to deassert the interrupt, which the
driver does not currently implement, therefore it needs fixing.

Update the driver to use ISR1 register set, fixing current
implementation.

Fixes: 8c39d710 ("PCI: aardvark: Add Aardvark PCI host controller driver")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=196339


Signed-off-by: Victor Gu <xigu@marvell.com>
[Thomas: tweak commit log.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
[lorenzo.pieralisi@arm.com: updated the commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Evan Wang <xswang@marvell.com>
Reviewed-by: Nadav Haklai <nadavh@marvell.com>
Cc: <stable@vger.kernel.org>