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/am65x_evm_r5_usbdfu_defconfig b/configs/am65x_evm_r5_usbdfu_defconfig
index f0dfc75..dbda4f7 100644
--- a/configs/am65x_evm_r5_usbdfu_defconfig
+++ b/configs/am65x_evm_r5_usbdfu_defconfig
@@ -31,6 +31,10 @@
 CONFIG_SPL_BSS_MAX_SIZE=0xc00
 CONFIG_SPL_STACK_R=y
 CONFIG_SPL_SEPARATE_BSS=y
+CONFIG_SYS_SPL_MALLOC=y
+CONFIG_HAS_CUSTOM_SPL_MALLOC_START=y
+CONFIG_CUSTOM_SYS_SPL_MALLOC_ADDR=0x84000000
+CONFIG_SYS_SPL_MALLOC_SIZE=0x1000000
 CONFIG_SPL_EARLY_BSS=y
 CONFIG_SPL_DMA=y
 CONFIG_SPL_ENV_SUPPORT=y