[roll third_party/pigweed] pw_kvs: Expand flash tests of alignment and write size

Add unit test support for flash alighment of 1 and decouple flash write
size from flash alignment. This allows downstream projects to better
configure on-device tests.

Make flash test parameter defines explicit with no default values.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/52526

third_party/pigweed Rolled-Commits: 630663b6351330c..2d4fa78d91e9cb9
Roller-URL: https://ci.chromium.org/b/8841867036310871504
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8841867036310871504
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I67c9aca8de8b01ace4e28dbfdbda331dbe1660b4
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/52843
Reviewed-by: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 630663b..2d4fa78 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 630663b6351330c5997e3aedc869a831303b5930
+Subproject commit 2d4fa78d91e9cb9f65c0dcaebc6ebfae8350953f