Add option to flip face buttons

[denizonm]

Add option to make the buttons a<->b x<->y, please.

Sunshine Version: 0.21.0.5bca024.dirty
Moonlight Embedded version: 2.6.2
Moonlight Embedded source: Comes with jelos
Moonlight Embedded running on: RGB30
Moonlight Embedded running on distribution: JELOS

for some reason the gamepad mapping flip the face buttons by default, the only way to fix being an edited gamecontrollerdb.txt (i could only get this fix working on arkos and not jelos but i am probably missing something)

[cgutman]

Which gamepad?