Update to BearSSL 0.6+ release, add AES_CCM modes (#5164)

Pull in latest BearSSL head (0.6 + minor additions) release and add AES_CCM
modes to the encryption options. Enable the aes_ccm initialization in client/server

The EC mul20 and square20 code was identical in two different files,
but because these copies were static, we ended up with an extra 6k of
duplicated code. Updated BearSSL to make them shared, saving 6KB.

tools/sdk/include/bearssl/bearssl_pem.h

@@ -236,6 +236,57 @@ br_pem_decoder_name(br_pem_decoder_context *ctx)
 	return ctx->name;
 }
 
+/**
+ * \brief Encode an object in PEM.
+ *
+ * This function encodes the provided binary object (`data`, of length `len`
+ * bytes) into PEM. The `banner` text will be included in the header and
+ * footer (e.g. use `"CERTIFICATE"` to get a `"BEGIN CERTIFICATE"` header).
+ *
+ * The length (in characters) of the PEM output is returned; that length
+ * does NOT include the terminating zero, that this function nevertheless
+ * adds. If using the returned value for allocation purposes, the allocated
+ * buffer size MUST be at least one byte larger than the returned size.
+ *
+ * If `dest` is `NULL`, then the encoding does not happen; however, the
+ * length of the encoded object is still computed and returned.
+ *
+ * The `data` pointer may be `NULL` only if `len` is zero (when encoding
+ * an object of length zero, which is not very useful), or when `dest`
+ * is `NULL` (in that case, source data bytes are ignored).
+ *
+ * Some `flags` can be specified to alter the encoding behaviour:
+ *
+ *   - If `BR_PEM_LINE64` is set, then line-breaking will occur after
+ *     every 64 characters of output, instead of the default of 76.
+ *
+ *   - If `BR_PEM_CRLF` is set, then end-of-line sequence will use
+ *     CR+LF instead of a single LF.
+ *
+ * The `data` and `dest` buffers may overlap, in which case the source
+ * binary data is destroyed in the process. Note that the PEM-encoded output
+ * is always larger than the source binary.
+ *
+ * \param dest     the destination buffer (or `NULL`).
+ * \param data     the source buffer (can be `NULL` in some cases).
+ * \param len      the source length (in bytes).
+ * \param banner   the PEM banner expression.
+ * \param flags    the behavioural flags.
+ * \return  the PEM object length (in characters), EXCLUDING the final zero.
+ */
+size_t br_pem_encode(void *dest, const void *data, size_t len,
+	const char *banner, unsigned flags);
+
+/**
+ * \brief PEM encoding flag: split lines at 64 characters.
+ */
+#define BR_PEM_LINE64   0x0001
+
+/**
+ * \brief PEM encoding flag: use CR+LF line endings.
+ */
+#define BR_PEM_CRLF     0x0002
+
 #ifdef __cplusplus
 }
 #endif