OvmfPkg/ResetSystemLib: rename to BaseResetSystemLib

OvmfPkg/ResetSystemLib: rename to BaseResetSystemLib

In preparation for introducing DxeResetSystemLib, rename the current
(only) ResetSystemLib instance to BaseResetSystemLib.

In the DSC files, keep the ResetSystemLib resolution in the same
[LibraryClasses] section, but move it near the TimerLib resolution, as the
differences between the ResetSystemLib instances will mostly follow those
seen under OvmfPkg/Library/AcpiTimerLib.

(While OvmfXen does not use "OvmfPkg/Library/AcpiTimerLib", perform the
same movement there too, for keeping future DSC diffing simple.)

Cc: Anthony Perard <anthony.perard@citrix.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Julien Grall <julien@xen.org>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Cc: Rebecca Cran <rebecca@bsdio.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2675
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20200417153751.7110-6-lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
Reviewed-by: Rebecca Cran <rebecca@bsdio.com>