Convert CONFIG_CMD_PCI to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_PCI

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
diff --git a/configs/beaver_defconfig b/configs/beaver_defconfig
index 10fd50d..aaea936 100644
--- a/configs/beaver_defconfig
+++ b/configs/beaver_defconfig
@@ -19,6 +19,7 @@
 CONFIG_CMD_USB_MASS_STORAGE=y
 # CONFIG_CMD_FPGA is not set
 CONFIG_CMD_GPIO=y
+CONFIG_CMD_PCI=y
 # CONFIG_CMD_SETEXPR is not set
 # CONFIG_CMD_NFS is not set
 CONFIG_CMD_EXT4_WRITE=y