ARM: zynq: Extend malloc size

SPL DM MMC FAT requires more malloc space(3k fat buffers + dm)
that it is available now. Extend SPL malloc space.

Current OCM layout:
0xffff0000 - 0xfff2000 - Full malloc space
0xffff2000 - 0xffff300 - Stack location
0xfffff300 - CONFIG_SYS_MALLOC_F_LEN - Early malloc space
0xfffffd00 - sizeof(GD) - GD
0xfffffe00 - 0xffffffff - SoC specific boot code
Signed-off-by: NMichal Simek <michal.simek@xilinx.com>

include/configs/zynq-common.h

@@ -369,7 +369,7 @@
 
 /* On the top of OCM space */
 #define CONFIG_SYS_SPL_MALLOC_START	OCM_HIGH_ADDR
-#define CONFIG_SYS_SPL_MALLOC_SIZE	0x1000
+#define CONFIG_SYS_SPL_MALLOC_SIZE	0x2000
 
 /*
  * SPL stack position - and stack goes down