Enable PCIe for Khadas VIM3 (#3092) (#3100)

It seems that the PCIe driver is not enabled for Khadas VIM3. Enable it
by default.

Note to make use of the M2X extension board, the following commands need
to be executed on the U-Boot command line:

```
HAOS> i2c dev 0
Setting bus to 0
HAOS> i2c mw 0x18 0x33 1
```

buildroot-external/board/khadas/kernel-vim.config

@@ -160,7 +160,7 @@ CONFIG_PCI_IOV=y
 CONFIG_HOTPLUG_PCI=y
 CONFIG_PCI_HOST_GENERIC=y
 CONFIG_PCIE_DW_PLAT_HOST=y
-# CONFIG_PCI_MESON is not set
+CONFIG_PCI_MESON=y
 CONFIG_DEVTMPFS=y
 CONFIG_DEVTMPFS_MOUNT=y
 CONFIG_SIMPLE_PM_BUS=y