net: phy: nxp-c45-tja11xx: run cable test with the PHY in test mode

For TJA1120, the enable bit for cable test is not writable if the PHY is
not in test mode.

Signed-off-by: Radu Pirea (NXP OSS) <radu-nicolae.pirea@oss.nxp.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20230731091619.77961-10-radu-nicolae.pirea@oss.nxp.com


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