MAINTAINERS: remove me as maintainer for I2C host drivers

The number of I2C host controller drivers keeps increasing, and although
I had some success acquiring specific driver maintainers, my bandwidth
is by far not enough to act as a fallback for the rest of the drivers.
To reflect this status-quo in MAINTAINERS, add a separate entry for I2C
host drivers, let the I2C list (= community) be the contact point, and
mark this section as "Odd fixes".

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>