ANDROID: build.config.allmodconfig: Enable hermetic builds

This was previously not possible due to the lack of kernel module
signing support in BoringSSL.

Said support has now landed in Kernel Build Tools.

Fixes: bce40b72 ("ANDROID: Disable hermetic toolchain for allmodconfig builds")
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Change-Id: Ideddac33d8d79f2819a9f68e3e80a0b045e58907
(cherry picked from commit 055fcf75)