ANDROID: gki_defconfig: enabled UAPI header compile testing

To ensure UAPI headers will compile standalone and can (later) be
monitored for API/ABI stability, enable the feature accordingly.

That seams like an additional overhead at compile time, but runs
smoothly while we are waiting for the LTO link to finish :-)

Bug: 73298553
Signed-off-by: Matthias Maennich <maennich@google.com>
Change-Id: Iae4f67f430ee2a3000f9f035aa0cd4392e72460f
(cherry picked from commit 9465730798f95fc5a0f0916ef6bcdfc7a1e839e9)