mfd: sta2x11-mfd: Add sta2x11_mfd_get_regs_data() function

A couple of predefined clocks (mux and gated) need to be
initialized with the virtual address of the clock's controlling
register and the address of a spinlock used to protect against
races.

This function exports such data for all the mfd cells.

Signed-off-by: Davide Ciminaghi <ciminaghi@gnudd.com>
Acked-by: Alessandro Rubini <rubini@gnudd.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>