mfd: syscon: atmel-smc: Add helper to retrieve register layout

For HSMC controller, the register layout depends on the device i.e. the
offset of setup, pulse, cycle, mode and timings registers is not the
same. An helper is added to provide the correct register layout.

Fixes: fe9d7cb2 ("mfd: syscon: atmel-smc: Add new helpers to ease
SMC regs manipulation")
Suggested-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>