runqemu.in: qemu-system-ppc is required in build directory

Conditional check has been added for qemu-system-ppc in
$STAGING_BINDIR_NATIVE folder so that for qemuppc it would
pickup the qemu-system-ppc from STAGING_BINDIR_NATIVE.

JIRA: SB-4106

Signed-off-by: Sujith H <Sujith_Haridasan@mentor.com>
Merge pull request #385 from sharidas/qemuppc-fix

runqemu.in: qemu-system-ppc is required in build directory