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/imx8mm_data_modul_edm_sbc_defconfig b/configs/imx8mm_data_modul_edm_sbc_defconfig
index 5a67bbf..b76f4c4 100644
--- a/configs/imx8mm_data_modul_edm_sbc_defconfig
+++ b/configs/imx8mm_data_modul_edm_sbc_defconfig
@@ -42,6 +42,7 @@
 CONFIG_ARCH_MISC_INIT=y
 CONFIG_BOARD_LATE_INIT=y
 CONFIG_SPL_MAX_SIZE=0x25000
+CONFIG_SPL_BSS_MAX_SIZE=0x2000
 # CONFIG_SPL_RAW_IMAGE_SUPPORT is not set
 CONFIG_SPL_LEGACY_IMAGE_FORMAT=y
 CONFIG_SPL_LEGACY_IMAGE_CRC_CHECK=y