mmio: add 16-bit variants of read/write/set

Change-Id: If4fb5585865768daa151bd4aa343ac5c84d2e9c3
i2c: clean-up in progress

 - use read16/write16/set16 from mmio.h to access I2C registers.

Change-Id: Ic221e6134e024ea0a6690f21cff208a728286948
splash: framebuffer test program

Change-Id: I7e045a4c6cec476615057f46f530693c0a2a17e0
splash: use parameters provided by the fb driver

Certain parameters, such as screen resolution, differ between
monitors. Enhance the splash program to dynamically configure
itself.

Change-Id: I49b0a3704decb7cb4633a1ee424b0419a1d67cf0