imx6-sabresd: Improve the explanation of the fragment file

Improve the explanation of the need for using the performance governor.

This problem is specific to mx6sabresd board and the Egalax touchscreen
running a mainline kernel, so make this clear.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

board/freescale/imx6-sabresd/linux_qt5.fragment

@@ -1,4 +1,4 @@
-# Currently kernel mainline exhibits issues when running cpufreq as ondemand
-# governor on mx6.
+# Currently mx6sabresd exhibits touchscreen issues when running cpufreq as
+# ondemand governor with a mainline kernel.
 # CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND is not set
 CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE=y