ARM: omap2plus_defconfig: use CONFIG_CPUFREQ_DT

commit 40d1746d2eeec5e05956d749cca6364573b472b6 upstream.

CONFIG_GENERIC_CPUFREQ_CPU0 disappeared with commit bbcf071969b20f
("cpufreq: cpu0: rename driver and internals to 'cpufreq_dt'")

Use the renamed CONFIG_CPUFREQ_DT generic driver. It looks like with
v3.18-rc1, commit bbcf071969b20f and fdc509b15eb3eb came in via
different trees causing the resultant v3.18-rc1 to be non-functional for
cpufreq as default supported with omap2plus_defconfig.

Fixes: fdc509b15eb3eb ("ARM: omap2plus_defconfig: Add cpufreq to defconfig")
Signed-off-by: Nishanth Menon <nm@ti.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>