devel/SDL2: Use the GLESv2+EGL video driver instead of the RPI video driver
on Raspberry Pi.

This allows RetroArch to be used on ARM NetBSD again (seemingly, when the
rgui menu driver is used). Previously, SDL2 would fail to produce shared
libraries when linked against the Broadcom libraries, which would cause
problems when linking against certain applications (notably RetroArch).

While here, disable options properly.

(nia)