eglinfo: Refactor & Add EGL_EXT_explicit_device support
As a part of implementing EGL_EXT_explicit_device[1] support in mesa, having some way of making the relevant query in eglinfo came in handy.
In order to neatly add this support, refactor the support for EGL_EXT_platform_base too.
[1] https://registry.khronos.org/EGL/extensions/EXT/EGL_EXT_explicit_device.txt