i2c: octeon: Add platform prefix to macros

The macros for TWSI register's offset are generically
named, rename them to be platform specific macros by
adding 'OCTEON_REG' as prefix.

Signed-off-by: Piyush Malgujar <pmalgujar@marvell.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>