cpufreq: armada-37xx: Fix the AVS value for load L1

cpufreq: armada-37xx: Fix the AVS value for load L1

The original CPU voltage value for load L1 is too low for Armada 37xx SoC
when base CPU frequency is 1000 or 1200 MHz. It leads to instabilities
where CPU gets stuck soon after dynamic voltage scaling from load L1 to L0.

Update the CPU voltage value for load L1 accordingly when base frequency is
1000 or 1200 MHz. The minimal L1 value for base CPU frequency 1000 MHz is
updated from the original 1.05V to 1.108V and for 1200 MHz is updated to
1.155V. This minimal L1 value is used only in the case when it is lower
than value for L0.

This change fixes CPU instability issues on 1 GHz and 1.2 GHz variants of
Espressobin and 1 GHz Turris Mox.

Marvell previously for 1 GHz variant of Espressobin provided a patch [1]
suitable only for their Marvell Linux kernel 4.4 fork which workarounded
this issue. Patch forced CPU voltage value to 1.108V in all loads. But
such change does not fix CPU instability issues on 1.2 GHz variants of
Armada 3720 SoC.

During testing we come to the conclusion that using 1.108V as minimal
value for L1 load makes 1 GHz variants of Espressobin and Turris Mox boards
stable. And similarly 1.155V for 1.2 GHz variant of Espressobin.

These two values 1.108V and 1.155V are documented in Armada 3700 Hardware
Specifications as typical initial CPU voltage values.

Discussion about this issue is also at the Armbian forum [2].

[1] - https://github.com/MarvellEmbeddedProcessors/linux-marvell/commit/dc33b62c90696afb6adc7dbcc4ebbd48bedec269
[2] - https://forum.armbian.com/topic/10429-how-to-make-espressobin-v7-stable/

Signed-off-by: Pali Rohár <pali@kernel.org>
Acked-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Tested-by: Tomasz Maciej Nowak <tmn505@gmail.com>
Tested-by: Anders Trier Olesen <anders.trier.olesen@gmail.com>
Tested-by: Philip Soares <philips@netisense.com>
Fixes: 1c3528232f4b ("cpufreq: armada-37xx: Add AVS support")
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>