Add pico_set_modified_binary_type function

[will-v-pi]

This adds a function to create binaries using an existing binary type & linker script, but with modified RAM/SCRATCH addresses

A similar function is already in use by the encrypted bootloader example, and picotool xip_ram_perms binary, so this extends those by adding scratch address modification

For example, to only use SRAM1 so you can power down SRAM0 in your binary you could use

pico_set_modified_binary_type(<my_exe> default RAM "0x20040000" "256k")

To create a XIP_SRAM only binary you could use

pico_set_modified_binary_type(<my_exe> no_flash
    RAM "0x13ffc000" "12k"
    SCRATCH_X "0x13fff000" "2k"
    SCRATCH_Y "0x13fff800" "2k")

The existing memmap_blocked_ram.ld could be created using

pico_set_modified_binary_type(<my_exe> default RAM "0x21000000" "256k")