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/thuban_defconfig b/configs/thuban_defconfig
index 2f0a1c6..0a6b0e8 100644
--- a/configs/thuban_defconfig
+++ b/configs/thuban_defconfig
@@ -37,6 +37,9 @@
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_ARCH_MISC_INIT=y
 CONFIG_SPL_BSS_START_ADDR=0x80000000
+CONFIG_SYS_SPL_MALLOC=y
+CONFIG_HAS_CUSTOM_SPL_MALLOC_START=y
+CONFIG_CUSTOM_SYS_SPL_MALLOC_ADDR=0x80208000
 CONFIG_SPL_I2C=y
 CONFIG_SPL_NAND_DRIVERS=y
 CONFIG_SPL_NAND_ECC=y