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/sandbox_defconfig b/configs/sandbox_defconfig
index 698ced0..3fe2702 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -40,6 +40,7 @@
 CONFIG_CMD_USB=y
 CONFIG_CMD_REMOTEPROC=y
 CONFIG_CMD_GPIO=y
+CONFIG_CMD_PCI=y
 CONFIG_CMD_TFTPPUT=y
 CONFIG_CMD_TFTPSRV=y
 CONFIG_CMD_RARP=y