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/imx6dl_mamoj_defconfig b/configs/imx6dl_mamoj_defconfig
index 6f249db..7e6e3bb 100644
--- a/configs/imx6dl_mamoj_defconfig
+++ b/configs/imx6dl_mamoj_defconfig
@@ -17,6 +17,7 @@
 CONFIG_LTO=y
 CONFIG_DISTRO_DEFAULTS=y
 CONFIG_BOOTDELAY=3
+CONFIG_SYS_SPL_MALLOC=y
 CONFIG_SPL_OS_BOOT=y
 CONFIG_SPL_FALCON_BOOT_MMCSD=y
 CONFIG_SYS_MMCSD_RAW_MODE_KERNEL_SECTOR=0x1000