drm: mcde: Fix display initialization problem

The following bug appeared in the MCDE driver/display
initialization during the recent merge window.

First the place we call drm_fbdev_generic_setup() in the
wrong place: this needs to be called AFTER calling
drm_dev_register() else we get this splat:

 ------------[ cut here ]------------
WARNING: CPU: 0 PID: 1 at ../drivers/gpu/drm/drm_fb_helper.c:2198 drm_fbdev_generic_setup+0x164/0x1a8
mcde a0350000.mcde: Device has not been registered.
Modules linked in:
Hardware name: ST-Ericsson Ux5x0 platform (Device Tree Support)
[<c010e704>] (unwind_backtrace) from [<c010a86c>] (show_stack+0x10/0x14)
[<c010a86c>] (show_stack) from [<c0414f38>] (dump_stack+0x9c/0xb0)
[<c0414f38>] (dump_stack) from [<c0121c8c>] (__warn+0xb8/0xd0)
[<c0121c8c>] (__warn) from [<c0121d18>] (warn_slowpath_fmt+0x74/0xb8)
[<c0121d18>] (warn_slowpath_fmt) from [<c04b154c>] (drm_fbdev_generic_setup+0x164/0x1a8)
[<c04b154c>] (drm_fbdev_generic_setup) from [<c04ed278>] (mcde_drm_bind+0xc4/0x160)
[<c04ed278>] (mcde_drm_bind) from [<c04f06b8>] (try_to_bring_up_master+0x15c/0x1a4)
(...)

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200613223027.4189309-1-linus.walleij@linaro.org