arm: at91: siemens: Add support to generate combined SPL+U-Boot image

arm: at91: siemens: Add support to generate combined SPL+U-Boot image

This patch adds the necessary defines to the Siemens AT91SAM based
boards (smartweb, corvus and taurus) to generate the combined binary
image with SPL and main U-Boot image combined (u-boot-with-spl.bin).

Signed-off-by: Stefan Roese <[email protected]>
Cc: Heiko Schocher <[email protected]>
Cc: Andreas Bießmann <[email protected]>
Cc: Eugen Hristev <[email protected]>
Reviewed-by: Heiko Schocher <[email protected]>
Tested on the taurus board:
Tested-by: Heiko Schocher <[email protected]>