* machine/rp2350: add flash support for rp2350
* combine duplicate files
* clean things up and group by source file
* add stubbed out xip cache clean func if needed in the future
* update flash_enable_xip_via_boot2
* remove unused macros and fix inconsistent formatting
* make flash size configurable like rp2040
* add missing flash size configs
* retain big Go CGo compatibility per #4103
* clarify CS0_SIZE source and remove single-use typedef
Michael Smith
soypat