cpufreq: dt: Fix sysfs duplicate filename creation for platform-device

ti-cpufreq and cpufreq-dt-platdev drivers are registering platform-device
with same name "cpufreq-dt" using platform_device_register_*() routines.
This is leading to build warnings appended below.

Providing hardware information to OPP framework along with the platform-
device creation should be done by ti-cpufreq driver before cpufreq-dt
driver comes into place.

This patch add's TI am33xx, am43 and dra7 platforms (which use opp-v2
property) to the blacklist of devices in cpufreq-dt-platform driver to
avoid creating platform-device twice and remove build warnings.

[    2.370167] ------------[ cut here ]------------
[    2.375087] WARNING: CPU: 0 PID: 1 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x58/0x78
[    2.383112] sysfs: cannot create duplicate filename '/devices/platform/cpufreq-dt'
[    2.391219] Modules linked in:
[    2.394506] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.13.0-next-20170912 #1
[    2.402006] Hardware name: Generic A...