ARM: at91: sama5: add common environment for QSPI

Use the same memory layout as we use for the NAND boot on the other boards.

QSPI flashes are present on the following boards:
sama5d2_xplained RevB:  32 Mbyte flash (mx25l3273fm2i-08g)
sama5d2_xplained RevC:   8 Mbyte flash (sst26vf064b-104i/sn)
sama5d27_som1_ek:        8 Mbyte flash (sst26vf064b-104i/sn)
sama5d2_ptc_ek:          8 Mbyte flash (sst26vf064b-104i/sn)

The 8 Mbyte limit is enough to cope with the memory layout used in the NAND
boot. rootfs exceeds the 8 Mbyte limit and will stay in eMMC in the
sama5d2_xplained case. The final scope is to use a single memory layout for
all boot medias.

Signed-off-by: Cyrille Pitchen <cyrille.pitchen@microchip.com>
[tudor.ambarus@microchip.com: change memory layout, add commit message]
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>