Updated keyboard map to match Atomulator and ignored fake shift sequences which prevented shift working with arrow keys

Change-Id: I5144543fab6f466b6042af7961e2c708062d1dd8
F1,2,3,4 now set clock to 1,2,4,8MHz; refactored cpu_clken to be a register to improve timing

Change-Id: I5e26998421461ff8cf0a0c4a603f44a68e4ee469