net: enetc: fix the netc-lib driver build dependency

The kernel robot reported the following errors when the netc-lib driver
was compiled as a loadable module and the enetc-core driver was built-in.

ld.lld: error: undefined symbol: ntmp_init_cbdr
referenced by enetc_cbdr.c:88 (drivers/net/ethernet/freescale/enetc/enetc_cbdr.c:88)
ld.lld: error: undefined symbol: ntmp_free_cbdr
referenced by enetc_cbdr.c:96 (drivers/net/ethernet/freescale/enetc/enetc_cbdr.c:96)

Simply changing "tristate" to "bool" can fix this issue, but considering
that the netc-lib driver needs to support being compiled as a loadable
module and LS1028 does not need the netc-lib driver. Therefore, we add a
boolean symbol 'NXP_NTMP' to enable 'NXP_NETC_LIB' as needed. And when
adding NETC switch driver support in the future, there is no need to
modify the dependency, just select "NXP_NTMP" and "NXP_NETC_LIB" at the
same time.

Reported-by: Arnd Bergmann <arnd@kernel.org>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202505220734.x6TF6oHR-lkp@intel.com/


Fixes: 4701073c ("net: enetc: add initial netc-lib driver to support NTMP")
Suggested-by: Arnd Bergmann <arnd@kernel.org>
Signed-off-by: Wei Fang <wei.fang@nxp.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>