Only a few drivers rely on the CAN rx offload framework (as of the
writing of this patch, only four: flexcan, m_can, mcp251xfd and
ti_hecc). Split it out of can-dev and add a new config symbol:
CAN_RX_OFFLOAD.

The drivers relying on CAN rx offload are in different sub
folders. Make CAN_RX_OFFLOAD an hidden option and tag all the drivers
depending on that feature with "select CAN_RX_OFFLOAD" so that the
option gets automatically enabled if and only if one of those drivers
is chosen.

Link: https://lore.kernel.org/all/20220610143009.323579-5-mailhol.vincent@wanadoo.frSuggested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Acked-by: Max Staudt <max@enpas.org>
Tested-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>