offb: Fix setting of the pseudo-palette for >8bpp

When using a >8bpp framebuffer, offb advertises truecolor, not directcolor,
and doesn't touch the color map even if it has a corresponding access method
for the real hardware.

Thus it needs to set the pseudo-palette with all 3 components of the color,
like other truecolor framebuffers, not with copies of the color index like
a directcolor framebuffer would do.

This went unnoticed for a long time because it's pretty hard to get offb
to kick in with anything but 8bpp (old BootX under MacOS will do that and
qemu does it).

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: stable@kernel.org
Signed-off-by: Nizar Lazuardy Firmansyah <nizar.digital@gmail.com>
offb: Fix bug in calculating requested vram size

We used to try to request 8 times more vram than needed, which would
fail if the card has a too small BAR (observed with qemu & kvm).

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: stable@kernel.org
Signed-off-by: Nizar Lazuardy Firmansyah <nizar.digital@gmail.com>