vga-switcheroo: make PCI dependency explicit

This driver depends on the PCI infrastructure, but the dependency has
not been explicitly called out.

Fixes: 5d32a665 ("PCI/ACPI: Allow ACPI to be built without CONFIG_PCI set")
Signed-off-by: Sinan Kaya <okaya@kernel.org>
Reviewed-by: Lukas Wunner <lukas@wunner.de>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>