Documentation/powerpc: Add proper links for manual and tests

The links that are mentioned in this document are no longer
valid. So changed the proper links for NXGZIP user manual and
test cases.
Reported-by: Bulent Abali <abali@us.ibm.com>
Signed-off-by: Haren Myneni <haren@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/08511c1e92ac239f20ac88c73c59d1f8cf02e6ad.camel@linux.ibm.com

Documentation/powerpc/vas-api.rst

@@ -254,7 +254,7 @@ using this window. the signal will be issued to the thread group leader
 signals.
 
 NX-GZIP User's Manual:
-https://github.com/libnxz/power-gzip/blob/master/power_nx_gzip_um.pdf
+https://github.com/libnxz/power-gzip/blob/master/doc/power_nx_gzip_um.pdf
 
 Simple example
 ==============
@@ -301,5 +301,5 @@ Simple example
 			close(fd) or window can be closed upon process exit
 		}
 
-	Refer https://github.com/abalib/power-gzip for tests or more
+	Refer https://github.com/libnxz/power-gzip for tests or more
 	use cases.