boards: amlogic: Add FriendlyElec NanoPi K2 board support

This adds platform code for the FriendlyElec NanoPi K2 board based on a
Meson GXBB (S905) SoC with the Meson GXBB configuration.

This initial submission only supports:
- UART
- MMC/SDCard
- Ethernet
- Reset Controller
- Clock controller

Cc: Yuefei Tan <yftan@friendlyarm.com>
Signed-off-by: Thomas McKahan <tonymckahan@gmail.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>

configs/nanopi-k2_defconfig

@@ -0,0 +1,40 @@
+CONFIG_ARM=y
+CONFIG_ARCH_MESON=y
+CONFIG_SYS_TEXT_BASE=0x01000000
+CONFIG_MESON_GXBB=y
+CONFIG_TARGET_NANOPI_K2=y
+CONFIG_DEBUG_UART_BASE=0xc81004c0
+CONFIG_DEBUG_UART_CLOCK=24000000
+CONFIG_IDENT_STRING=" nanopi-k2"
+CONFIG_DEFAULT_DEVICE_TREE="meson-gxbb-nanopi-k2"
+CONFIG_DEBUG_UART=y
+CONFIG_OF_BOARD_SETUP=y
+# CONFIG_DISPLAY_CPUINFO is not set
+# CONFIG_DISPLAY_BOARDINFO is not set
+# 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_SETEXPR is not set
+CONFIG_CMD_REGULATOR=y
+CONFIG_OF_CONTROL=y
+CONFIG_NET_RANDOM_ETHADDR=y
+CONFIG_DM_GPIO=y
+CONFIG_DM_I2C=y
+CONFIG_SYS_I2C_MESON=y
+CONFIG_DM_REGULATOR=y
+CONFIG_DM_REGULATOR_FIXED=y
+CONFIG_DM_RESET=y
+CONFIG_DM_MMC=y
+CONFIG_MMC_MESON_GX=y
+CONFIG_DM_ETH=y
+CONFIG_ETH_DESIGNWARE=y
+CONFIG_PINCTRL=y
+CONFIG_PINCTRL_MESON_GXBB=y
+CONFIG_DEBUG_UART_MESON=y
+CONFIG_DEBUG_UART_ANNOUNCE=y
+CONFIG_DEBUG_UART_SKIP_INIT=y
+CONFIG_MESON_SERIAL=y
+CONFIG_OF_LIBFDT_OVERLAY=y