cargo.bbclass: show PACKAGECONFIG_CONFARGS in bbnote

cargo.bbclass: show PACKAGECONFIG_CONFARGS in bbnote

* PACKAGECONFIG_CONFARGS was added in:
  https://git.openembedded.org/openembedded-core/commit/?id=16745b20452de60ae2474433cc1a2fb1ed9f6a64
  but it wasn't added in bbnote above which might lead to confusing errors like I got now:

  NOTE: cargo build -v --frozen --target aarch64-webos-linux-gnu --release --manifest-path=.../git//Cargo.toml
  error: unexpected argument '--cfg' found

  Usage: cargo build --verbose... --frozen --target [<TRIPLE>] --release --manifest-path <PATH>

  and was wondering where --cfg came from.

* it was from recipe where we already use:
  RUSTFLAGS:append = " ${PACKAGECONFIG_CONFARGS}"
  it will be difficult to use PACKAGECONFIG for RUSTFLAGS and prevent
  them to be used here for cargo as well, what about the recipes which
  need them to explicitly append them to CARGO_BUILD_FLAGS ?

Signed-off-by: Martin Jansa <martin.jansa@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>