ARM: at91: sama5: update the spi flash mapping

ARM: at91: sama5: update the spi flash mapping

Also move the spi flash configurations to the at91-sama5_common.h.

Current at91 zImage size is about 3.3M, the old mapping is not
suitable. So update the spi flash map as following:
	0x0      ~ 0x004000: at91bootstrap(16k)
	0x04000  ~ 0x008000: u-boot env(16k)
	0x08000  ~ 0x060000: u-boot(352k)
	0x60000  ~ 0x06c000: dtb (48k)
	0x6c000  ~ 0x400000: kernel (3M+592k)

In AT91Bootstrap, the U-Boot in spi flash also update to 0x8000, refer
to following commit in AT91Bootstrap:
	3e91e54 Kconfig: fix spi flash address

So also update SPL's u-boot load address to 0x8000 in spi flash.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
Reviewed-by: Jagan Teki <jteki@openedev.com>