Use the sdk pkg-config when building gen_touchpad_hash.
Use the sdk pkg-config when building gen_touchpad_hash.

`gen_touchpad_hash` is compiled to run on the builder, so use pkg-config
from the builder to avoid races such as openssl not being installed for
the target when it is installed for the SDK.

BRANCH=none
BUG=b:257362347
TEST=emerge-strongbad chromeos-ec # and strongbad-cq passes

Change-Id: I59464cda5b1842b9aafc20244e4218f8a80f7442
Signed-off-by: Allen Webb <880184b418addffb87cd9c8e8e882ca6764ac96b@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/4006181
Reviewed-by: Gregory Nisbet <afc3bca0abcb2567b0a2495a821fca959b52ca27@google.com>
Code-Coverage: Zoss <345cf107e82c70959d46f59d98bddc98ce458aff@prod.google.com>
Reviewed-by: George Engelbrecht <c828e237e346dc3df684bcfc0b60e48b180f6a3d@google.com>
Reviewed-by: Jack Rosenthal <d3f605bef1867f59845d4ce6e4f83b8dc9e4e0ae@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec