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/sama5d3xek_spiflash_defconfig b/configs/sama5d3xek_spiflash_defconfig
index 2754920..ae47d92 100644
--- a/configs/sama5d3xek_spiflash_defconfig
+++ b/configs/sama5d3xek_spiflash_defconfig
@@ -42,6 +42,8 @@
 CONFIG_SPL_BSS_MAX_SIZE=0x80000
 # CONFIG_SPL_SHARES_INIT_SP_ADDR is not set
 CONFIG_SPL_STACK=0x318000
+CONFIG_SYS_SPL_MALLOC=y
+CONFIG_SYS_SPL_MALLOC_SIZE=0x80000
 CONFIG_SPL_DM_SPI_FLASH=y
 CONFIG_SPL_SPI_LOAD=y
 CONFIG_SYS_SPI_U_BOOT_OFFS=0x10000