MIPS/GAS: Correct `mips-*-sysv4*' target emulation configuration

MIPS/GAS: Correct `mips-*-sysv4*' target emulation configuration

Use `mips-*-sysv4*' rather than `mips-*-sysv4*MP*' to match the system
type for System V Release 4 MIPS targets, removing a GAS target
selection failure:

Assembler messages:
Fatal error: selected target format 'elf32-bigmips' unknown

on any assembly attempt with `mips-sysv4' and equivalent target
configurations.  These would typically be called `mips-sni-sysv4'
(Sinix) vs `mips-dde-sysv4.2MP' (Supermax).

This corrects commit 8614eeee67f9 ("Traditional MIPS patches"),
<https://sourceware.org/ml/binutils/2000-07/msg00018.html>, making GAS
target selection match commit dd745cfae548 ("Traditional MIPS patches"),
<https://sourceware.org/ml/binutils/2000-07/msg00018.html>, and commit
3548145dcbf6 ("Traditional MIPS patches"),
<https://sourceware.org/ml/binutils/2000-07/msg00018.html>, which added
support for these targets to BFD and LD respectively.

	gas/
	* configure.tgt: Use `mips-*-sysv4*' rather than
	`mips-*-sysv4*MP*'.