* Update SDRAM init timings to intermittent 8-flash SDRAM init errors
on some boards.
See: https://github.com/raspberrypi/rpi-eeprom/issues/67
* config: Fix missing initialisation of selected_expr to 1 in config.txt
Without an [all] section the new expression filter might default to
false. This impacts the bootloader early parsing of config.txt
for things like boot_ramdisk rather than the later config.txt pass
for device-tree parsing.
* config_loader: Add support [boot_partition=N] as an expression filter
The boot_partition tests whether the partition number N matches
the number that the system is booting from. This expression is
only supported in config.txt and is designed to make it easier
to have common boot.img ramdisks in an A/B system where the
conditional loads a different cmdline.txt file depending on
which partition boot.img is loaded from.
