arch,base,cpu: Split arch/pcstate.hh out of arch/types.hh.

The only thing brought in by arch/types.hh is TheISA::PCState. Instead
of having the other types around where they could be used accidentally,
and to make it more obvious what's being exported, this change splits
PCState out into a new switching header called arch/pcstate.hh. The
original arch/types.hh is no longer a switching header, and includes
pcstate.hh.

Change-Id: I8dfd298349e4565f316f7b9a028703289ada6010
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40177
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>

src/arch/SConscript

@@ -61,7 +61,7 @@ env.SwitchingHeaders(
         isa.hh
         locked_mem.hh
         page_size.hh
-        types.hh
+        pcstate.hh
         vecregs.hh
         '''),
     env.subst('${TARGET_ISA}'))