staging: fsl-dpaa2/ethsw: Fix tag control information value overwrite

The tag control information (TCI) part of the VLAN header contains several
fields, including PCP (priority code point) and PVID (port VLAN id).

Current implementation uses function ethsw_port_set_tci() to set the PVID
value and mistakenly overwrites the rest of the TCI fields with 0,
including PCP which by default has a value of 7.

Fix this by adding support to retrieve TCI set in hardware. Read existing
value and only updated the PVID fields, leaving others unchanged.

Signed-off-by: Razvan Stefanescu <razvan.stefanescu@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>