vf6xx: set vector table to memory

Set Vector Table Offset to memory location of our vector table.
Since we put the whole programm including the vector table into
memory, we need to make use of the Cortex-M4 system control block
Vector Table Offset Register (VTOR).
vf6xx: initial memorymap and clock control module

Add initial memorymap for Vybrid VF6xx module. Also add the clock
control module which allows to control system clocks and enable
clocks of individual pheripherials.
vf6xx: doc: initial commit

Add documentation Makefile and DoxygenLayout for Freescale Vybrid
VF6xx support.
vf6xx: enable floating-point coprocessor
vf6xx: calculate core clocks

Extend the clock controller module with a function to calculate
core clocks from the current registers settings. On Vybrid, we
assume that the core clocks are setup by the main operating system
running on the Cortex-A5. Nevertheless we need to know their actual
values in order to calculate other clocks or baud rates.

Verified on a Colibri VF61, which calculates following values:
ccm_core_clk: 500210526
ccm_platform_bus_clk: 166736842
ccm_ipg_bus_clk: 83368421