i2c-omap: convert 'rev1' flag to generic 'rev' u8

i2c-omap discriminates only between "revision 1" or "greater than
revision 1."  A following patch introduces code that must also
discriminate between rev2.x, rev3.6, and rev3.12 controllers.  Support
this by storing the full revision data from the I2C_REV register, rather
than just a single bit.

The revision definitions may need to be extended for other ES levels
that aren't currently available here.  rev3.6 is what's present on the
2430SDP here (unknown ES revision); rev3.12 is used on the 3430ES2
here.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>