staging: mt7621-dts: properly organize pcie node

Device tree pcie node for this SoC is using different
styles in its different properties. Hence properly
unify them to be able to write a a proper yaml schema
documentation.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20210505121736.6459-11-sergio.paracuellos@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>