pcmcia: allow PCMCIA support independent of the architecture

There is nothing architecture specific in the PCMCIA core, so allow
building it everywhere.  The actual host controllers will depend on ISA,
PCI or a specific SOC.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Dominik Brodowski <linux@dominikbrodowski.net>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Paul Burton <paul.burton@mips.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>