freedreno: add dummy fd_bo_from_fbdev implementation when KGSL is disabled

Make sure that this function is defined (even empty/dummy) when KGSL support is
disabled, since it's part of the driver i/f and it was reported to cause symbols
issues when building against musl libc implementation.

Reported-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Nicolas Dechesne <nicolas.dechesne@linaro.org>
Signed-off-by: Rob Clark <robclark@freedesktop.org>