* 2712d0: Enable background refresh on 2712d0 for all SDRAM sizes
This provides a minor performance benefit.
* Update GPT to support 4K native sectors
Bootloader logic updated to correctly interpret the GPT layout format specific to 4K native sector drives.
* recovery: Use ROM boot-mode flag to detect rpiboot mode
In recovery-mode use the bootrom register flag to detect the
original boot-mode rather than looking at whether the rpiboot
usb-device boot driver is initialised.
