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/mx6memcal_defconfig b/configs/mx6memcal_defconfig
index d555dbf..a1bc95b 100644
--- a/configs/mx6memcal_defconfig
+++ b/configs/mx6memcal_defconfig
@@ -15,6 +15,7 @@
 CONFIG_SYS_MEMTEST_START=0x10000000
 CONFIG_SYS_MEMTEST_END=0x20000000
 CONFIG_SUPPORT_RAW_INITRD=y
+CONFIG_SYS_SPL_MALLOC=y
 CONFIG_SPL_USB_HOST=y
 CONFIG_SPL_WATCHDOG=y
 CONFIG_HUSH_PARSER=y