Bug#851778: change CONFIG_FB from 'm' to 'y' on arm64

[Leif Lindholm <leif.lindholm@linaro.org>]

Package: linux-image-arm64
Version: 4.9+78
Severity: wishlist

Linux commit 9822504c1, included in v4.7, introduced EFI framebuffer
support on arm/arm64.

The Debian arm64 kernel config currently explicitly sets CONFIG_FB to
'm', overriding the defconfig 'y'. Since CONFIG_FB_EFI is "depends on
(FB = y)", this means we don't get efifb support on arm64. So could we
flip it to 'y', please?

This would also be a nice thing to do on armhf, but affect fewer
platforms.