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/pcm058_defconfig b/configs/pcm058_defconfig
index 54bef4e..132942b 100644
--- a/configs/pcm058_defconfig
+++ b/configs/pcm058_defconfig
@@ -30,6 +30,7 @@
 CONFIG_BOOTCOMMAND="run mmcboot;run nandboot"
 CONFIG_DISPLAY_BOARDINFO_LATE=y
 CONFIG_SPL_BOARD_INIT=y
+CONFIG_SYS_SPL_MALLOC=y
 CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR=0x18a
 CONFIG_SPL_DMA=y
 CONFIG_SPL_FS_EXT4=y