board: amlogic: vim3: add support for dynamic PCIe enable

The VIM3 on-board  MCU can mux the PCIe/USB3.0 shared differential
lines using a FUSB340TMX USB 3.1 SuperSpeed Data Switch between
an USB3.0 Type A connector and a M.2 Key M slot.
The PHY driving these differential lines is shared between
the USB3.0 controller and the PCIe Controller, thus only
a single controller can use it.

This adds this dynamic switching right before booting Linux
and the configuration steps in the boards documentation.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Tested-by: Kevin Hilman <khilman@baylibre.com>
[narmstrong: fixed warning by replacing min() by min_t()]
diff --git a/configs/khadas-vim3_defconfig b/configs/khadas-vim3_defconfig
index ee59904..df2d5bd 100644
--- a/configs/khadas-vim3_defconfig
+++ b/configs/khadas-vim3_defconfig
@@ -17,6 +17,7 @@
 # CONFIG_CMD_BDI is not set
 # CONFIG_CMD_IMI is not set
 CONFIG_CMD_GPIO=y
+CONFIG_CMD_I2C=y
 # CONFIG_CMD_LOADS is not set
 CONFIG_CMD_MMC=y
 CONFIG_CMD_SF_TEST=y
@@ -28,6 +29,8 @@
 CONFIG_OF_CONTROL=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_NET_RANDOM_ETHADDR=y
+CONFIG_DM_I2C=y
+CONFIG_SYS_I2C_MESON=y
 CONFIG_DM_MMC=y
 CONFIG_MMC_MESON_GX=y
 CONFIG_MTD=y