Add support for the Arcom/Eurotech Viper SBC CompactFlash card slot

The Arcom/Eurotech Viper needs some extra care to run. On this board,
the PC104 connector is actually wired to the second PCMCIA slot.
Therefore, this second socket needs to be enabled, despite not being
managed by the PCMCIA code.

I'd rather have the MECR setup in the platform support code so I could,
for example, use the PC104 bus without having the PCMCIA module loaded.

Signed-off-by: Marc Zyngier <marc.zyngier@altran.com>