The Debian packaging of mbedtls is maintained in git, using the
merging workflow described in dgit-maint-merge(7).  There isn't a
patch queue that can be represented as a quilt series.

A detailed breakdown of the changes is available from their canonical
representation - git commits in the packaging repository.  For
example, to see the changes made by the Debian maintainer in the first
upload of upstream version 1.2.3, you could use:

    % git clone https://git.dgit.debian.org/mbedtls
    % cd mbedtls
    % git log --oneline 1.2.3..debian/1.2.3-1 -- . ':!debian'

(If you have dgit, use `dgit clone mbedtls`, rather than plain `git
clone`.)

A single combined diff, containing all the changes, follows.
--- mbedtls-2.14.1.orig/include/mbedtls/bn_mul.h
+++ mbedtls-2.14.1/include/mbedtls/bn_mul.h
@@ -636,7 +636,8 @@
            "r6", "r7", "r8", "r9", "cc"         \
          );
 
-#elif defined (__ARM_FEATURE_DSP) && (__ARM_FEATURE_DSP == 1)
+#elif (__ARM_ARCH >= 6) && \
+    defined (__ARM_FEATURE_DSP) && (__ARM_FEATURE_DSP == 1)
 
 #define MULADDC_INIT                            \
     asm(
