can: Kconfig: add more information about Intel EG20T PCH CAN controller

Current menu description, not easy to understand what the description
means. So, add information about the device.

Signed-off-by: Tomoya MORINAGA <tomoya.rohm@gmail.com>
[mkl: Added space before opening parentheses in Kconfig.
      Make commit message more descriptive.]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>