GPIOMUXServer: Use new pin access control function

This commit updates the GPIOMUXServer to use the new access control
mechanisms that the seL4GPIOServer provides.

trivial: Update old comment

GPIOMUXServer: Refactor client-server interface

Use the connector definitions to control interface configuration and
initialization.

Provide an ADL API for creating the GPIOServer client-server interface
in any component.

Provide an ADL API for creating the MUXServer client-server interface in
any component.

GPIOMUXServer: Use the GPIO level constants

Instead of using confusing integer values for representing the two
different levels of a GPIO, this commit changes it so that the server
now uses the level constants (GPIO_LEVEL_HIGH/LOW) defined in
libplatsupport.

components: Add new GPIOMUXServer

This commit adds in a new CAmkES component: GPIOMUXServer. The component
is intended to multiplex the MUX and GPIO functionalities of a platform.
The component also includes a client library which abstracts over
libplatsupport/libplatsupportports and exposes the necessary constants
needed to interact with the component. At the moment, the server has
pretty basic functionality and only has exynos5 and tx2 support.