staging: tidspbridge: use scm functions to set boot address and mode

Instead of ioremapping SCM registers, use the correspondent layer
to write into them.

This allows us to get rid of a layer violation, since the registers
are no longer touched by driver code.

Signed-off-by: Omar Ramirez Luna <omar.ramirez@copitl.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>