arm: use the correct prototype for reset_cpu function

Align reset_cpu function with the next prototypes in
sysreset.h or in cpu_func.h to solve compilation issue:

  void reset_cpu(void);

This patch solves the prototype conflict when cpu_func.h is
included.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
4 files changed