[RCAR] Fix block device performance decreased

[RCAR] Fix block device  performance decreased

* After the RCAR BSP 5.5.O, the block device performance decreased.

The root cause is a change in the default kernel configuration of the BSP
(CPU Frequency scaling) from (RCAR BSP 4.7.0):

CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE=y
\# CONFIG_CPU_FREQ_DEFAULT_GOV_SCHEDUTIL is not set

To its new default (RCAR BSP 5.5.0)

\# CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE is not set
CONFIG_CPU_FREQ_DEFAULT_GOV_SCHEDUTIL=y

You can check current value at runtime using:

cat /sys/devices/system/cpu/cpufreq/policy0/scaling_governor
cat /sys/devices/system/cpu/cpufreq/policy4/scaling_governor

To mediate the regression we do switch back to the PERFORMANCE governor.

Bug-AGL: SPEC-4205

Signed-off-by: Ronan Le Martret <ronan.lemartret@iot.bzh>
Change-Id: I6d19d92dae9dd8c7977e2034215fce07d8318773
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/27108
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Tested-by: Jenkins Job builder account