matroxfb: add Matrox MGA-G200eW board support

It's needed to support the onboard video on my Spectre-free
Atom S1260 server board.

Signed-off-by: Rich Felker <dalias@libc.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
[b.zolnierkie: patch description fixup]
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200125195506.GA16638@brightrain.aerifal.cx