arm64: dts: imx8: align thermal node names with bindings

Bindings expect thermal node names to end with '-thermal':

  imx8qxp-mek.dtb: thermal-zones: 'pmic-thermal0' does not match any of the regexes: '^[a-zA-Z][a-zA-Z0-9\\-]{1,12}-thermal$', 'pinctrl-[0-9]+'

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>