powerpc: vdso: Make vdso32 installation conditional in vdso_install

powerpc: vdso: Make vdso32 installation conditional in vdso_install

The 32-bit vDSO is not needed and not normally built for 64-bit
little-endian configurations.  However, the vdso_install target still
builds and installs it.  Add the same config condition as is normally
used for the build.

Fixes: e0d005916994 ("powerpc/vdso: Disable building the 32-bit VDSO ...")
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Gbp-Pq: Topic bugfix/powerpc
Gbp-Pq: Name powerpc-vdso-make-vdso32-installation-conditional-in.patch