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/kontron_pitx_imx8m_defconfig b/configs/kontron_pitx_imx8m_defconfig
index 7b0d6b9..f8e11f5 100644
--- a/configs/kontron_pitx_imx8m_defconfig
+++ b/configs/kontron_pitx_imx8m_defconfig
@@ -31,6 +31,7 @@
 CONFIG_BOARD_LATE_INIT=y
 CONFIG_MISC_INIT_R=y
 CONFIG_SPL_MAX_SIZE=0x1f000
+CONFIG_SPL_BSS_MAX_SIZE=0x2000
 CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_USE_SECTOR=y
 CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR=0x300
 CONFIG_SPL_I2C=y