Do not check VINTF if no files

Do not check VINTF integrity / compatibility if
no files are built to /system/etc/vintf/* or /vendor/etc/vintf/*.

Test: m check-vintf-all on gsi_gms_arm64
Test: m check-vintf-all on coral

Fixes: 147749718
Fixes: 148007775

Change-Id: I874d1558e0b891b9d307eec536b1071d382a43f5