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/imx6q_bosch_acc_defconfig b/configs/imx6q_bosch_acc_defconfig
index 4b75e57..a2501eb 100644
--- a/configs/imx6q_bosch_acc_defconfig
+++ b/configs/imx6q_bosch_acc_defconfig
@@ -34,6 +34,7 @@
 CONFIG_BOOTCOMMAND="run mmc_mmc_fit"
 CONFIG_SPL_BOARD_INIT=y
 CONFIG_SPL_RAW_IMAGE_SUPPORT=y
+CONFIG_SYS_SPL_MALLOC=y
 CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR=0xaa
 # CONFIG_SPL_CRC32 is not set
 # CONFIG_SPL_CRYPTO is not set