
Add porting layer for PKCS7 parser on top of MbedTLS PKCS7 library. Introduce _LEGACY and _MBEDTLS kconfigs for PKCS7 parser legacy and MbedTLS implementations respectively. Signed-off-by: Raymond Mao <raymond.mao@linaro.org> Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>