Use CPU constraints from @pigweed

Uses new constraints in @pigweed to eliminate references to
@pw_toolchain.

Bug: b/346388161
Change-Id: Ifd69c30000dae0e6b5b110a7529a8a160cb2f506
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/quickstart/bazel/+/258952
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed-service-accounts.iam.gserviceaccount.com>
Presubmit-Verified: CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com>
Pigweed-Auto-Submit: Armando Montanez <amontanez@google.com>
Reviewed-by: Ted Pudlik <tpudlik@google.com>
diff --git a/targets/rp2/BUILD.bazel b/targets/rp2/BUILD.bazel
index bacbd17..437b656 100644
--- a/targets/rp2/BUILD.bazel
+++ b/targets/rp2/BUILD.bazel
@@ -49,7 +49,7 @@
         "@pico-sdk//bazel/constraint:rp2040",
         # For toolchain selection.
         "@platforms//cpu:armv6-m",
-        "@pw_toolchain//constraints/arm_mcpu:cortex-m0",
+        "@pigweed//pw_build/constraints/arm:cortex-m0",
     ],
     flags = flags_from_dict({
         "@pico-sdk//bazel/config:PICO_DEFAULT_LINKER_SCRIPT": "@pigweed//targets/rp2040:rp2040_linker_script",
@@ -64,7 +64,7 @@
         "@pico-sdk//bazel/constraint:rp2350",
         # For toolchain selection.
         "@platforms//cpu:armv8-m",
-        "@pw_toolchain//constraints/arm_mcpu:cortex-m33",
+        "@pigweed//pw_build/constraints/arm:cortex-m33",
     ],
     flags = flags_from_dict({
         "@pico-sdk//bazel/config:PICO_DEFAULT_LINKER_SCRIPT": "@pigweed//targets/rp2040:rp2350_linker_script",