Activate the device before attempt to access any of its registers.  Without
this change we may end up with a panic (Fatal kernel mode data abort:
'External Non-Linefetch Abort (S)') as described in
http://e2e.ti.com/support/arm/sitara_arm/f/791/t/276862.aspx.

It is now possible to bring up I2C1 and I2C2 on BBB.

Approved by:	adrian (mentor)
Bring the RPi I2C driver in line with ti_i2c.  Make it treat any slave
address as a 7-bit address.

Approved by:	adrian (mentor)