device.rs code conditional on ARM should probably not be

[jrmuizel]

There are a bunch of places in device.rs where we have things like
cfg!(any(target_arch="arm", target_arch="aarch64"))

arm seems like the wrong thing for these to be testing for. I suspect that these should actually be tests for opengles.

[jrmuizel]

e.g. in gecko we use GL_LUMINANCE on all platforms instead of GL_RED or GL_ALPHA