misc: Delete the now unnecessary create methods.

Most create() methods are no longer necessary. This change deletes them,
and occasionally moves some code from them into the constructors they
call.

Change-Id: Icbab29ba280144b892f9b12fac9e29a0839477e5
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/36536
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/dev/serial/uart8250.cc

@@ -319,9 +319,3 @@ Uart8250::unserialize(CheckpointIn &cp)
     if (txintrwhen != 0)
         schedule(txIntrEvent, txintrwhen);
 }
-
-Uart8250 *
-Uart8250Params::create() const
-{
-    return new Uart8250(*this);
-}