epiphany-hal-api: Adhere to new style function prototypes

Add 'void' to functions without arguments as per the format of new
style function prototypes. This silences warnings generated by
-Wfstrict-prototypes, which is used in systems like setup.py and
generally anal compilers.
Merge branch 'hal' of https://github.com/WillDignazio/epiphany-libs into WillDignazio-hal
Merge branch 'WillDignazio-hal'