UBUNTU: [Config] Disable CONFIG_I2C_THUNDERX

UBUNTU: [Config] Disable CONFIG_I2C_THUNDERX

BugLink: https://bugs.launchpad.net/bugs/1696937
The support for IPMI system interface on Cavium ThunderX (bug #1688132)
has been added to Xenial kernel as a module compiled for arm64, so the
config for the -snapdragon kernel needs to be updated to explicitly
disable this module, otherwise the -snapdragon package build fails.

Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Acked-by: Andy Whitcroft <apw@canonical.com>
Acked-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>