zynq: Add support for U-BOOT SPL

SPL is using ps7_init.c/h files which are generated
from design tools which have to be copied to
boards/xilinx/zynq folder before compilation.

BSS section is moved to SDRAM because fat support
requires more space than SRAM size.

Added:
- MMC and QSPI support
- Boot OS directly from SPL
- Enable SPL command

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Tom Rini <trini@ti.com>
diff --git a/board/xilinx/zynq/Makefile b/board/xilinx/zynq/Makefile
index 6301a8c..3f19a1c 100644
--- a/board/xilinx/zynq/Makefile
+++ b/board/xilinx/zynq/Makefile
@@ -6,3 +6,4 @@
 #
 
 obj-y	:= board.o
+obj-$(CONFIG_SPL_BUILD)	+= ps7_init.o