source org: move pdp1 to dec folder

src/mame/mame.lst

@@ -34525,7 +34525,7 @@ tetriskr                        // (c) 1988? bootleg
 @source:amstrad/pda600.cpp
 pda600                          //
 
-@source:pdp1/pdp1.cpp
+@source:dec/pdp1.cpp
 pdp1                            // 1961 DEC PDP1
 
 @source:dec/pdp11.cpp

src/mame/mess.flt

@@ -198,6 +198,7 @@ dec/decstation.cpp
 dec/dectalk.cpp
 dec/decwritr.cpp
 dec/jensen.cpp
+dec/pdp1.cpp
 dec/pdp11.cpp
 dec/rainbow.cpp
 dec/vax11.cpp
@@ -592,7 +593,6 @@ pc/ps2.cpp
 pc/sis630.cpp
 pc/tandy1t.cpp
 pc/tosh1000.cpp
-pdp1/pdp1.cpp
 philips/odyssey2.cpp
 philips/p2000t.cpp
 philips/vg5k.cpp