PCI: meson: Build as module by default

Enable pci-meson to build as a module whenever ARCH_MESON is enabled.

Link: https://lore.kernel.org/r/20200918181251.32423-1-khilman@baylibre.com


Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Cc: Yue Wang <yue.wang@amlogic.com>