Move sh_vendor cflags to its own target

Move sh_vendor cflags to its own target

The cc_defaults.vendor doesn't work due to VNDK being disabled.
(b/69133815). So, the conversion to soon caused the sh_vendor to start
using $PATH from the environment (instead of the hardcoded one) that in
turn caused vendor shell scripts trying to run system toybox commands.

Bug: 68771183
Test: m -j sh_vendor; adb sync; adb shell; /vendor/bin/sh; echo $PATH
Test: Boot marlin with no denials from init_radio, init_power domains.
Change-Id: Ia90b74a4cffdeba9b53f3b8fb8a56c98386794fa
Signed-off-by: Sandeep Patil <sspatil@google.com>