i2c: Adds a functions set that supports flexible addressing.

The current I2C API provides inline functions to access 1 byte
register addresses. This commit adds a set of I2C inline functions
as shortcuts to handle:

- 16 bit register addressing. A family of functions that allows to
  handle 2 byte register addressing and can receive the address
  parameter as a simple variable. This allows a developer to handle
  the address as a C constant or macro.

- Multiple byte addressing. A family of functions to access
  registers with a configurable register address size. This family
  of functions handle register addressing of any size but receives
  the address parameter as a byte array.

Change-Id: Id369ab9eaad7eea807554371d3a520f67dc2e0f2
Signed-off-by: Juan Manuel Cruz Alcaraz <juan.m.cruz.alcaraz@intel.com>