video: pci: Set up the copy framebuffer

When using a copy framebuffer we need to tell the video subsystem its
address. U-Boot's normally allocated framebuffer is used as the working
buffer, but nothing is displayed until it is copied to the copy
framebuffer.

For this to work the video driver must request that a framebuffer be
allocated separately from the hardware framebuffer, so add a check for
that.

Also add a log category so that logging appears correctly.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Anatolij Gustschin <agust@denx.de>
Tested-by: Bin Meng <bmeng.cn@gmail.com>