cpufreq: BOOST: Adjust setting of BOOST frequency just before first valid freq

cpufreq: BOOST: Adjust setting of BOOST frequency just before first valid freq

Before this change the BOOST frequency was always hardcoded to be the
highest one. This worked for M0 and Proxima, but failed when support for
odroid U3 has been added.

Since odroid U3 supports three more freqs, higher than the boost for M0,
it is necessary to adjust setting of boost frequency. Without that on M0
cpufreq sets frequencies reserved for odroid, which is dangerous.

Change-Id: I70b19453d5853b6c0139f2c59c98dd5ad65da01e
Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>