Convert CONFIG_SYS_SPL_MALLOC_SIZE et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_SPL_MALLOC_SIZE
   CONFIG_SYS_SPL_MALLOC_START

We introduce a default value here as well, and CONFIG_SYS_SPL_MALLOC to
control if we have a malloc pool or not.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/gardena-smart-gateway-at91sam_defconfig b/configs/gardena-smart-gateway-at91sam_defconfig
index ea79a2f..a253b13 100644
--- a/configs/gardena-smart-gateway-at91sam_defconfig
+++ b/configs/gardena-smart-gateway-at91sam_defconfig
@@ -42,6 +42,8 @@
 CONFIG_SPL_SYS_MALLOC_SIMPLE=y
 # CONFIG_SPL_SHARES_INIT_SP_ADDR is not set
 CONFIG_SPL_STACK=0x308000
+CONFIG_SYS_SPL_MALLOC=y
+CONFIG_SYS_SPL_MALLOC_SIZE=0x80000
 # CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_USE_SECTOR is not set
 CONFIG_SPL_NAND_SUPPORT=y
 CONFIG_SPL_NAND_RAW_ONLY=y