arm/acpi: fix PCI _PRT definition

arm/acpi: fix PCI _PRT definition

The address field in each _PRT mapping package should be constructed
with high word for device# and low word for function#, so it is wrong
to use bus_no as the high word. The existing code adds a bunch useless
entries with device #s above 31. Enumerate all possible slots
(i.e. PCI_SLOT_MAX) instead.

Signed-off-by: Heyi Guo <[email protected]>
Reviewed-by: Michael S. Tsirkin <[email protected]>
Message-id: 20200204014325[email protected]
Signed-off-by: Peter Maydell <[email protected]>