lantiq: fix thermal sensors driver

Read the temperature including the decimale place from the CGU_GPHY1_CR
register.

Decrement the temperature read from the register by 38.0 degree celsius.
The temperature range of the sensor is -38.0 to +154 °C and the register
value 0 is equal to -38.0 °C. This fixes the report of unrealistic
temperatures as seen on all tested boards.

Give the SoC a few milliseconds to get the first temperature value. On
some rare occasions there is no temperature value in the register when
read the first time after activation. This leads to a reported
temperature of -38.0 °C on boot.

Only version 1.2 of the vr9 SoC has a temperature sensor. Add a check
to make sure the driver doesn't load on v1.1 vr9 SoCs.

Signed-off-by: Mathias Kresin <dev@kresin.me>