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/pico-imx7d_bl33_defconfig b/configs/pico-imx7d_bl33_defconfig
index d814a42..d13336d 100644
--- a/configs/pico-imx7d_bl33_defconfig
+++ b/configs/pico-imx7d_bl33_defconfig
@@ -27,6 +27,7 @@
 CONFIG_USE_BOOTCOMMAND=y
 CONFIG_BOOTCOMMAND="run distro_bootcmd"
 CONFIG_SPL_MAX_SIZE=0xe000
+CONFIG_SPL_BSS_MAX_SIZE=0x100000
 CONFIG_SPL_I2C=y
 CONFIG_SPL_USB_HOST=y
 CONFIG_SPL_USB_GADGET=y