cpufreq-dt: add 'boost' mode frequencies support

cpufreq-dt: add 'boost' mode frequencies support

Add 'boost' mode frequencies support:
- add boost-opps binding to cpufreq-dt driver bindings
- make cpufreq_init() adjust freq_table accordingly
- fix set_target() to handle boost frequencies
- add boost_supported field to struct cpufreq_dt_platform_data
- set dt_cpufreq_driver.boost_supported in dt_cpufreq_probe()

This patch makes cpufreq-dt driver aware of 'boost' mode frequencies
and prepares it for adding support for Exynos4x12 'boost' support.

boost-opps binding is currently limited to cpufreq-dt but once there is
a need for cpufreq wide and/or generic Linux device support for 'boost'
mode cpufreq-dt can be updated to handle the new code without changing
the binding itself.

The decision to make 'boost' mode support limited to cpufreq-dt driver
for now was taken because 'boost' mode is currently a niche feature and
code needed for parsing boost-opps binding is minimal and simple.  More
generic (i.e. separate 'boost' OPPs list in struct device and generic
cpufreq convertion of them to freq_table format) support would need far
more code and effort to make it work.  Doing it without a demonstrated
real need would be on overengineering IMHO.

Cc: Tomasz Figa <tomasz.figa@gmail.com>
Cc: Mike Turquette <mturquette@linaro.org>
Cc: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Cc: Thomas Abraham <thomas.ab@samsung.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>