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/mccmon6_nor_defconfig b/configs/mccmon6_nor_defconfig
index 3718d08..1214163 100644
--- a/configs/mccmon6_nor_defconfig
+++ b/configs/mccmon6_nor_defconfig
@@ -24,6 +24,7 @@
 # CONFIG_USE_BOOTCOMMAND is not set
 CONFIG_BOARD_LATE_INIT=y
 CONFIG_SPL_BOARD_INIT=y
+CONFIG_SYS_SPL_MALLOC=y
 CONFIG_SPL_FIT_IMAGE_TINY=y
 CONFIG_SPL_ENV_SUPPORT=y
 CONFIG_SPL_NOR_SUPPORT=y