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/arch/mips/SConscript

@@ -38,7 +38,6 @@ if env['TARGET_ISA'] == 'mips':
     Source('isa.cc')
     Source('linux/linux.cc')
     Source('linux/se_workload.cc')
-    Source('mmu.cc')
     Source('pagetable.cc')
     Source('process.cc')
     Source('remote_gdb.cc')