They're still in the operating range according to i.MX 8M Quad
datasheet. There's some headroom added over minimal values to
account for voltage drop.

Operational ranges (min - typ - max [selected]):
 - VDD_SOC (BUCK1): 0.81 - 0.9 - 0.99 [0.88]
 - VDD_ARM (BUCK2): 0.81 - 0.9 - 1.05 [0.84] (1000MHz)
                    0.90 - 1.0 - 1.05 [0.93] (1500MHz)
 - VDD_GPU (BUCK3): 0.81 - 0.9 - 1.05 [0.85] (800MHz)
                    0.90 - 1.0 - 1.05 [ -- ] (1000MHz)
 - VDD_VPU (BUCK4): 0.81 - 0.9 - 1.05 [ -- ] (550/500/588MHz)
                    0.90 - 1.0 - 1.05 [0.93] (660/600/800MHz)

Idle power consumption doesn't appear to be influenced much,
but a simple load test (`cat /dev/urandom | pigz - > /dev/null`
combined with running Animatch) seems to show about 0.3W of
difference.

Care is advised, as there may be differences between each
units in how low can they be undervolted - in my experience,
reaching that point usually makes the phone fail to boot.
In my case, it appears that my Birch phone can go down the most.

This is a somewhat conservative set of values that I've seen
working well on all my devices; I haven't tried very hard to
optimize it, so more experiments are welcome.
Signed-off-by: Sebastian Krzyszkowiak <sebastian.krzyszkowiak@puri.sm>
Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>