[POWERPC] Update .gitignore for new vdso generated files

We now generate vdso[32,64].so.dbg as part of the build so
add them to .gitignore
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

arch/powerpc/kernel/vdso32/.gitignore

 vdso32.lds
+vdso32.so.dbg

arch/powerpc/kernel/vdso64/.gitignore

 vdso64.lds
+vdso64.so.dbg