yocto/parsec-se-driver: Pass recipe sysroot to bindgen

parsec-se-driver uses Rust's bindgen to generate C bindings to
MbedTLS. Explicitly pass the target sysroot to bindgen using
BINDGEN_EXTRA_CLANG_ARGS to prevent it from using host header files.

Signed-off-by: Peter Hoyes <peter.hoyes@arm.com>