[media] xc5000: Add support for 7MHz bandwidth for DVB-C/DVB-T

While xc5000 supports 7MHz bandwidth, the driver were lacking the code
implementing this feature, causing tuning issues with VHF chanels
used in Countries like Italy.

After this patch:

>>> tune to: 177500000:INVERSION_AUTO:BANDWIDTH_7_MHZ:FEC_2_3:FEC_AUTO:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_32:HIERARCHY_NONE
0x0000 0x0d49: pmt_pid 0x0102 RAI -- Rai 1 (running)
0x0000 0x0d4a: pmt_pid 0x0101 RAI -- Rai 2 (running)
0x0000 0x0d4b: pmt_pid 0x0100 RAI -- Rai 3 TGR Veneto (running)
0x0000 0x0d53: pmt_pid 0x0118 RAI -- Rai News (running)
0x0000 0x0d54: pmt_pid 0x0119 Rai -- Rai 3 TGR Emilia Romagna (running)
0x0000 0x0d4c: pmt_pid 0x0103 Rai -- Rai Radio1 (running)
0x0000 0x0d4d: pmt_pid 0x0104 Rai -- Rai Radio2 (running)
0x0000 0x0d4e: pmt_pid 0x0105 Rai -- Rai Radio3 (running)
Network Name 'Rai'

Tested-by: Eddi De Pieri <eddi@depieri.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>