ARM: at91: move alternative initial mapping to board-dt-sama5.c

For sama5d4, remove an indirection and the remaining need for at91_boot_soc
structure.
This will allow further cleanup.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>

diff --cc arch/arm/mach-at91/board-dt-sama5.c
Simple merge

diff --cc arch/arm/mach-at91/sama5d4.c
Simple merge

diff --cc arch/arm/mach-at91/setup.c
Simple merge