Update pico2 to use a toolset (swiftlang#120)

Updates the Makefile for pico2-neopixel to use a toolset instead of
hardcoding build flags into the makefile. Additionally moves the SVD
file for the pico2 into the Tools/SVDs folder and adds an rp2040 SVD.
Removes the need to set the TOOLCHAINS env for the pico2-neopixel
example.

Author: rauhul

Tools/SVDs/README.md

@@ -0,0 +1,8 @@
+# SVDs
+
+The SVDs used in this repo have been copied from the following sources.
+
+| file                 | source                                                               |
+|----------------------|----------------------------------------------------------------------|
+| `rp2040.patched.svd` | https://github.com/rp-rs/rp2040-pac/blob/main/svd/rp2040.svd.patched |
+| `rp2350.patched.svd` | https://github.com/rp-rs/rp235x-pac/blob/main/svd/RP2350.svd.patched |