dtv_demod: tl1,dvbc, new method for fast channel searching [1/1]

dtv_demod: tl1,dvbc, new method for fast channel searching [1/1]

PD#TV-2154

Problem:
[Hisense-T962X2-P-customer-DTV]:DVBC QAM is set to auto to search channels

Solution:
add new searching method
note:
use "demod_dvbc_speedup_en" to mark the new method
it's disabled as default, can be enabled if needed
we can make it always enabled after all testing are passed
enable: echo fast_search on > /sys/kernel/debug/demod/dvbc_channel_fast

Verify:
verified by t962x2_x301

Change-Id: Icaaab9f27eb058a062d7048c6ca9fa2e3bff008e
Signed-off-by: Zhiwei Yuan <zhiwei.yuan@amlogic.com>