Reduce BearSSL code size by not -O2 FSMs (#7807)

The FSMs that drive the encryption logic are not performance critical,
but they are very large.  Build BearSSL using -Os on them, leaving -O2
everywhere else (i.e. encryption) for speed.

Saves 1-2KB of flash for SSL applications.

tools/sdk/include/bearssl/bearssl_git.h

 // Do not edit -- Automatically generated by tools/sdk/ssl/bearssl/Makefile
-#define BEARSSL_GIT 28bebad
+#define BEARSSL_GIT c0b69df

bearssl @ c0b69dfb

-Subproject commit 28bebad56295df6a49b01ad323a6e354cb977785
+Subproject commit c0b69dfb837f0027180c72f13f7c90cfafb83c16