drm/fbdev-generic: Do not set physical framebuffer address

Framebuffer memory is allocated via vzalloc() from non-contiguous
physical pages. The physical framebuffer start address is therefore
meaningless. Do not set it.

The value is not used within the kernel and only exported to userspace
on dedicated ARM configs. No functional change is expected.

v2:
- refer to vzalloc() in commit message (Javier)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: a5b44c4a ("drm/fbdev-generic: Always use shadow buffering")
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Javier Martinez Canillas <javierm@redhat.com>
Cc: Zack Rusin <zackr@vmware.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: <stable@vger.kernel.org> # v6.4+
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Zack Rusin <zack.rusin@broadcom.com>
Reviewed-by: Sui Jingfeng <sui.jingfeng@linux.dev>
Tested-by: Sui Jingfeng <sui.jingfeng@linux.dev>
Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240419083331.7761-2-tzimmermann@suse.de