dpaa2: avoid linking objects into multiple modules

dpaa2: avoid linking objects into multiple modules

Each object file contains information about which module it gets linked
into, so linking the same file into multiple modules now causes a warning:

scripts/Makefile.build:254: drivers/net/ethernet/freescale/dpaa2/Makefile: dpaa2-mac.o is added to multiple modules: fsl-dpaa2-eth fsl-dpaa2-switch
scripts/Makefile.build:254: drivers/net/ethernet/freescale/dpaa2/Makefile: dpmac.o is added to multiple modules: fsl-dpaa2-eth fsl-dpaa2-switch

Change the way that dpaa2 is built by moving the two common files into a
separate module with exported symbols instead.

Tested-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Reviewed-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://patch.msgid.link/20260402184726.3746487-3-arnd@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>