ndk: Add AThermal_getThermalHeadroom

The SDK variant of this [PowerManager#getThermalHeadroom] was introduced in R,
but NDK support didn't make it in time.

Bug: b/168612028
Test: atest CtsThermalTestCases
Change-Id: I58422ca2567f6145e388fe669334a15c3a72c1e4
1 file changed