ARM: dts: msm: Set floor BW vote based on CPU freq for MSM8939

This will make sure that at any point of time BW vote will not
go below the limit set by mincpubw. cpubw node uses BIMC_MON governor
and will vote higher depends on the requirement. The bus driver will
aggregate votes and take the highest of these.

Change-Id: I8811857fc6714c79d9d0780e64ae4f4249ff5c5e
Signed-off-by: Arun KS <arunks@codeaurora.org>