Add GPIO configuration helper function

This commit adds a 'gpio_set_port_config' functions that allows user
to define all required pin configuration for a project in a single
table instead of using multiple 'gpio_set_mode' calls.
Add provisions to initialize clock tree

This commit adds functionality that would allow user to
define/initialize the clock tree configuration as a structure, which
allows for simpler and much more flexible clock initialization.
Merge pull request #9 from ndreys/staging

Add GPIO configuration helper function