i2c: wmt: create wmt_i2c_init for general init

Some common initialization actions are put in the function
wmt_i2c_init(), which is convenient to share with zhaoxin.

Reviewed-by: Andi Shyti <andi.shyti@kernel.org>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Hans Hu <hanshu-oc@zhaoxin.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>