Convert CONFIG_SPL_BSS_MAX_SIZE et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SPL_BSS_MAX_SIZE
   CONFIG_SPL_MAX_FOOTPRINT

Note that the da850evm platforms were violating the "only use one" rule
here, and so now hard-code their BSS limit.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/imx8mp_rsb3720a1_6G_defconfig b/configs/imx8mp_rsb3720a1_6G_defconfig
index bc7f310..223767b 100644
--- a/configs/imx8mp_rsb3720a1_6G_defconfig
+++ b/configs/imx8mp_rsb3720a1_6G_defconfig
@@ -35,6 +35,7 @@
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_BOARD_LATE_INIT=y
 CONFIG_SPL_MAX_SIZE=0x26000
+CONFIG_SPL_BSS_MAX_SIZE=0x400
 CONFIG_SPL_BOARD_INIT=y
 CONFIG_SPL_BOOTROM_SUPPORT=y
 CONFIG_SPL_SYS_MALLOC_SIMPLE=y