i2c: davinci: Split functions into two parts for future DM support

i2c: davinci: Split functions into two parts for future DM support

The i2c driver will be converted to support device model. In preparation
for that change split the various functions into two parts. This will
allow device model specific driver to reuse the majority of the code from
the non device model implementation.

Also rename the probe function to probe_chip to better reflect its
purpose.

Signed-off-by: Franklin S Cooper Jr <fcooper@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Heiko Schocher <hs@denx.de>