Moving to a better, default storage location

[oyama]

Currently, 128 KB is used as the default storage, avoiding the two sectors used by the BT flash storage(BT_BANK) at the end of the storage.
The location of the BT flash storage varies depending on the size of the on-board flash memory, but the RP2350 uses three sectors to support errata RP2350-E10.
raspberrypi/pico-sdk#2412

This creates confusion that the offset at which the kvstore image is written (picotool load -o <OFFSET>) varies finely from device to device.

Before:.

picotool load -o 0x101de000 kvs-image.bin # Pico
picotool load -o 0x103de000 kvs-image.bin # Pico2

After:

picotool load -o 0x101de000 kvs-image.bin # Pico
picotool load -o 0x103dd000 kvs-image.bin # Pico2

The change from only ending with de000 yields variations of de000 and dd000.

Wastes 1 sector of flash, but can be improved by using the position avoiding 3 sectors including BT flash storage as default storage.

After:

picotool load -o 0x101dd000 kvs-image.bin # Pico
picotool load -o 0x103dd000 kvs-image.bin # Pico2