1. Add 980 drv_usbd.
2. EMAC - move MDC CLK divider before EMAC initialization.
3. Correct NUC980 and M480 CAN RX_MSG_ID_INDEX definition.
4. add USBD cdc demo - vcom_echo.
5. mnt - add mount_table definition.

2.update README.md(add contact)

1. Fix porting driver.
2. Add NAU8822 audio codec driver.
3. Add NUC980 I2S porting driver.

Although the program elf is uploaded successfully, the upload message is
still "Remote communication error.“, but actually upload works.

After fix, it will be "[Inferior 1 (Remote target) detached]"

By the way, I also checked latest nuclei-sdk 0.3.0 release with latest
rt-thread source code
Signed-off-by: Huaqi Fang <578567190@qq.com>

1. Make up sources and bugfix.
2. Add nu_gpio_pin_get.
3. Add PM operator in USB host driver.
4. Support NUC980 stage 1 and add nk-980iot board.

Expand the COMM section