This patch refactors the MMIO routines in the GPIO and I2C drivers to
eliminate the base_addr parameter that specifies the MMIO base
address. Instead, just the MMIO routines themselves retrieve the base
address from the driver structure.
This patch adds the i2c.c, i2c.h and i2c-registers.h files,
which support access to I2C controller configuration register
through a function interface.