Fix the i2c bus speed divisors for TI OMAP4 and AM335x.

For OMAP4, the old values for 1MHz gave a bus frequency of about 890KHz.
The new numbers hit 1MHz exactly.

For AM335x the prescaler values are adjusted to give a 24MHz clock for
all 3 standard speeds, as the manual recommends (as near as we can tell,
there are errors and typos apparent in the document).  Also, 1MHz speed
is added, and has been tested successfully on a BeagleboneWhite board.

PR:		195009