net: fec: Refactor: Replace FEC_ENET_FCE with FEC_RCR_FLOWCTL

FEC_ENET_FCE is the Flow Control Enable bit (bit 5) of the RCR.
This is now defined as FEC_RCR_FLOWCTL.

Signed-off-by: Csókás Bence <csokas.bence@prolan.hu>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20240212153717.10023-2-csokas.bence@prolan.hu


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