libdrm: intel/Android.mk: Filter libdrm_intel library requirements on x86/x86_64

When building AOSP after updating libdrm project to the
freedesktop/master branch, I've seen the following build errors:

external/libdrm/intel/Android.mk: error: libdrm_intel
(SHARED_LIBRARIES android-arm64) missing libpciaccess
(SHARED_LIBRARIES android-arm64) You can set
ALLOW_MISSING_DEPENDENCIES=true in your environment if this is
intentional, but that may defer real problems until later in the
build.

Using ALLOW_MISSING_DEPENDENCIES=true when building allows
things to function properly, but is not ideal.

So basically, while I'm not including the libdrm_intel package
into the build, just the fact that the Android.mk file references
libpciaccess which isn't a repo included in AOSP causes the build
failure.

So it seems we need some sort of conditional filter in the
Android.mk to skip over it if we're not building for intel.

Cc: Chad Versace <chad.versace@linux.intel.com>
Cc: Marissa Wall <marissaw@google.com>
Cc: Sean Paul <seanpaul@google.com>
Cc: Dan Willemsen <dwillemsen@google.com>
Cc: Tomasz Figa <tfiga@google.com>
Cc: Robert Foss <robert.foss@collabora.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>