Boot: Add support for later versions of Mbed TLS

Fixes an issue that prevented the bootloader from supporting Mbed TLS
versions greater than 2.6.1.

This patch contains the changes made by the following two commits in
the upstream MCUboot repo at https://github.com/JuulLabs-OSS/mcuboot
 - Git SHA 33939929430a3e5375976fdb45ee71bc5fea0206
 - Git SHA 785dc4c9b3eb60968fac05b71af62e1b7ec563ac

Change-Id: I22a907e6a79e272ac5115d2e6940b850497eaf18
Signed-off-by: Jamie Fox <jamie.fox@arm.com>
1 file changed