staging: mt7621-dts: use 'interrupt-map' and 'interrupt-map-mask'

staging: mt7621-dts: use 'interrupt-map' and 'interrupt-map-mask'

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

This is not really necessary and code has been fixed to avoid
custom configuration of the virtual bridges and make possible
to properly map the root ports interrupts using this standard
properties. Hence properly update device tree accordly.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20210505121736.6459-10-sergio.paracuellos@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>