arm: zynq: Enable setup board name for different boards

There is no need to use zynq name as SYS_BOARD for all boards.
The patch is adding an option to change it.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/arch/arm/mach-zynq/Kconfig b/arch/arm/mach-zynq/Kconfig
index 8772904..1352359 100644
--- a/arch/arm/mach-zynq/Kconfig
+++ b/arch/arm/mach-zynq/Kconfig
@@ -36,6 +36,7 @@
 	  want to skip ddr init and this option is useful for it.
 
 config SYS_BOARD
+	string "Board name"
 	default "zynq"
 
 config SYS_VENDOR