reset: sti: add deassert counter in reset channel descriptor

reset: sti: add deassert counter in reset channel descriptor

This deassert counter allow to manage "shared" reset lines
encountered in some specific case. On STiH410 SoC, DWC3,
EHCI and OHCI are all using a respective PHY, but all of
these PHYs shared a "global" reset.

Currently, during command "usb stop", all host controller are
stopped (XHCI, EHCI and OHCI). XHCI is first shutdowned, which
means that PHY global reset is asserted. Then EHCI is shutdowned,
but its PHY reset has already been asserted which make handshake()
call failed in ehci_shutdown().

This counter allows to really assert a reset lines only when the
"last" user is asserting it.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>