net: wwan: iosm: fixes unnecessary doorbell send

In TX packet accumulation flow transport layer is
giving a doorbell to device even though there is
no pending control TX transfer that needs immediate
attention.

Introduced a new hpda_ctrl_pending variable to keep
track of pending control TX transfer. If there is a
pending control TX transfer which needs an immediate
attention only then give a doorbell to device.

Signed-off-by: M Chetan Kumar <m.chetan.kumar@linux.intel.com>
Reviewed-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>