RP2350: pad_checksum appears unused/misleading

[AnnsAnns]

It appears like the pad_checksum function accidentally sets the cpu as the cortex-m0plus, however the rp2350 uses the cortex-m33.

After further investigation, it appears like this entire script is completely misleading, based on chapter 5.9.5 of the RP2350 documentation the boot2 checksum is not needed for the rp2350:

Unlike RP2040, there is no requirement for flash binaries to have a checksummed "boot2" flash setup function at flash address 0. The RP2350 bootrom performs a simple best-effort XIP setup during flash scanning, and a flash-resident program can continue executing in this state, or can choose to reconfigure the QSPI interface at a later time for best performance.

I am not really sure how to proceed with this PR, wouldn't it make sense to completely get rid of that script based on the fact that this isn't something the pico2 actually needs?

[kilograham]

as per the PR, this actually may just want some removal of dead build code... certainly doesn't make any sense to do pad/checksum, but i'm not sure off the top of my head what is needed in terms of pico_define_boot_stage2 and friends)

moving to 2.2.0 as this is a more involved change (not the .cpu wasn't that important as the entire asm files is .byte)

[AnnsAnns]

Thank you for the update