arm: at91: arm926ejs/u-boot-spl.lds: Add _image_binary_end to SPL lds

arm: at91: arm926ejs/u-boot-spl.lds: Add _image_binary_end to SPL lds

This patch adds _image_binary_end to the SPL linker script. This will be
used be the upcoming GARDENA AT91SAM based platform, which uses DT in
SPL and configures CONFIGURE_SPL_SEPARATE_BSS.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Heiko Schocher <hs@denx.de>
Cc: Andreas Bießmann <andreas@biessmann.org>
Cc: Eugen Hristev <eugen.hristev@microchip.com>
Reviewed-by: Heiko Schocher <hs@denx.de>