ext: hal: altera: disable altera_avalon_i2c compilation warnings

Disable compilation warnings for altera_avalon_i2c.c as it is not
maintained in Zephyr.

Cmake does not allow us to use set_source_files_properties on
source files directly, these files need to be linked to either
a target executable or a target library. Due to the above reason,
altera_avalon_i2c CMakeLists.txt creates a library and links the
source file to the zephyr library.

Signed-off-by: Ramakrishna Pallala <ramakrishna.pallala@intel.com>