HID: mcp2200: added driver for GPIOs of MCP2200

Added a gpiochip compatible driver to control the 8 GPIOs of
the MCP2200 by using the HID interface.

Using GPIOs with alternative functions (GP0<->SSPND, GP1<->USBCFG,
GP6<->RXLED, GP7<->TXLED) will reset the functions, if set (unset by
default).

The driver was tested while also using the UART of the chip. Setting
and reading the GPIOs has no effect on the UART communication. However,
a reset is triggered after the CONFIGURE command. If the GPIO Direction
is constantly changed, this will affect the communication at low baud
rates. This is a hardware problem of the MCP2200 and is not caused by
the driver.

Signed-off-by: Johannes Roith <johannes@gnu-linux.rocks>
Reviewed-by: Rahul Rameshbabu <sergeantsagara@protonmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>