net: fec: add more macros for bits of FEC_ECR

There are also some RCR bits that are not defined but are used by the
driver, so add macro definitions for these bits to improve readability
and maintainability.

In addition, although FEC_RCR_HALFDPX has been defined, it is not used
in the driver. According to the description of FEC_RCR[1] in RM, it is
used to disable receive on transmit. Therefore, it is more appropriate
to redefine FEC_RCR[1] as FEC_RCR_DRT.

Signed-off-by: Wei Fang <wei.fang@nxp.com>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/20250711091639.1374411-3-wei.fang@nxp.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>