mmdevapi: Reorder a couple of functions to avoid forward declarations and make MMDevice_SetPropValue() static.

Unless the driver implements ARB_ES2_compatibility / GL4.1, FBO completeness
depends on what read / draw buffers are set.

For the benefit of depth-only draws and clears, that would otherwise fail FBO
completeness, unless the driver supports ARB_ES2_compatibility.

Anything that isn't explicitly specified is set to GL_NONE by
glDrawBuffersARB().

It's trivial, and allows the rest of the code to assume at least 1 render
target is present.

winex11: Move the SendMessage(WM_SYSCOMMAND, SC_MAXIMIZE/SC_RESTORE) call after the window extents check.