arm: zynq: Fix SPL SD boot mode

This patch is fixing two issues:
1. Insufficient stack size for fat fs buffers
2. Insufficient space in malloc area

Tested on zc702 and zc706.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/configs/zynq_zybo_defconfig b/configs/zynq_zybo_defconfig
index 4126460..21f8c08 100644
--- a/configs/zynq_zybo_defconfig
+++ b/configs/zynq_zybo_defconfig
@@ -2,6 +2,7 @@
 CONFIG_SYS_CONFIG_NAME="zynq_zybo"
 CONFIG_ARCH_ZYNQ=y
 CONFIG_SYS_TEXT_BASE=0x4000000
+CONFIG_SPL_STACK_R_ADDR=0x200000
 CONFIG_DEFAULT_DEVICE_TREE="zynq-zybo"
 CONFIG_DEBUG_UART=y
 CONFIG_FIT=y
@@ -9,6 +10,7 @@
 CONFIG_FIT_VERBOSE=y
 # CONFIG_DISPLAY_CPUINFO is not set
 CONFIG_SPL=y
+CONFIG_SPL_STACK_R=y
 CONFIG_SPL_OS_BOOT=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="Zynq> "