mfd: altera-sysmgr: Add SOCFPGA System Manager

The SOCFPGA System Manager register block aggregates different
peripheral functions into one area.
On 32 bit ARM parts, handle in the same way as syscon.
On 64 bit ARM parts, the System Manager can only be accessed by
EL3 secure mode. Since a SMC call to EL3 is required, this new
driver uses regmaps similar to syscon to handle the SMC call.

Since regmaps abstract out the underlying register access, the
changes to drivers accessing the System Manager are minimal.

Signed-off-by: Thor Thayer <thor.thayer@linux.intel.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>