V4L/DVB (5761): Fix broken b2c2 dependency on non x86 architectures

This patch moves flexcop-dma (currently used only by flexcop-pci) to
b2c2-flexcop-pci module, that is dependent on CONFIG_PCI, fixing the bug 
as reported by Geert Uytterhoeven <geert@linux-m68k.org>:

drivers/media/dvb/b2c2/flexcop-dma.c uses the PCI DMA API, but
DVB_B2C2_FLEXCOP doesn't depend on PCI, causing the following problem on
PCI-less systems:

| linux/drivers/media/dvb/b2c2/flexcop-dma.c:20: warning: implicit declaration of function 'pci_alloc_consistent'
| linux/drivers/media/dvb/b2c2/flexcop-dma.c:20: warning: implicit declaration of function 'pci_alloc_consistent'

Apparently this is the flexcop DMA core, which is used by both
DVB_B2C2_FLEXCOP_PCI and DVB_B2C2_FLEXCOP_USB.

Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>