staging: mt7621-pci: avoid custom 'map_irq' function

staging: mt7621-pci: avoid custom 'map_irq' function

Custom function for 'map_irq' was introduced in
commit fab6710e4c51 ("staging: mt7621-pci: fix PCIe interrupt mapping")

After some testing in an adquired device with a similar
pci layout that those that was having problems, I got
into a better way to solve the issue just using device tree
'interrupt-map' and 'interrupt-map-mask' properties. For
this to be possible we must avoid custom configuration of
the virtual bridges registers from driver code. Doing in
this way buses are not reconfigured so we can properly
use bus related bits and mask in device tree to map
correctly the interrupts. Hence remove custom configuration
of the bridges as well as custom 'map_irq' related stuff.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20210505121736.6459-8-sergio.paracuellos@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>