machine/rp2350: add flash support for rp2350 (#4803)

* 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

Author: mikesmitty

src/machine/flash.go

@@ -1,4 +1,4 @@
-//go:build nrf || nrf51 || nrf52 || nrf528xx || stm32f4 || stm32l4 || stm32wlx || atsamd21 || atsamd51 || atsame5x || rp2040
+//go:build nrf || nrf51 || nrf52 || nrf528xx || stm32f4 || stm32l4 || stm32wlx || atsamd21 || atsamd51 || atsame5x || rp2040 || rp2350
 
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