build: CONFIG_VGA_FIXUP_ASM should depend on CONFIG_BUILD_VGABIOS

Add the dependency to CONFIG_VGA_FIXUP_ASM so the menu option only
appears when appropriate.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
(cherry picked from commit f24eb2f853d4aa28814761e0bbc7df78149f8029)