test/power: fix CPU frequency check for intel_pstate

test/power: fix CPU frequency check for intel_pstate

For acpi_cpufreq and cppc_cpufreq, both cpuinfo_cur_freq and
scaling_cur_freq exist. For pstate, only scaling_cur_freq exists.
And value in scaling_cur_freq and cpuinfo_cur_freq may not be the
same. For acpi_cpufreq and cppc_cpufreq, we should check
cpuinfo_cur_freq but not scaling_cur_freq. So here change the
check sequence to make sure it works for all cpufreq drivers.
Besides, add rounding for pstate driver.

Fixes: ff6dfb8e492f ("test/power: fix CPU frequency check")
Cc: stable@dpdk.org
Signed-off-by: Richael Zhuang <richael.zhuang@arm.com>
Acked-by: David Hunt <david.hunt@intel.com>