mips: Consolidate INTERNAL_VSYSCALL_CALL

This patch consolidates the mips, mips64, and mips64-n32
INTERNAL_VSYSCALL_CALL on a single implementation.

No semantic changes. I checked against a build for mips-linux-gnu,
mips64-linux-gnu, and mips64-n32-linux-gnu.

	* sysdeps/unix/sysv/linux/mips/mips32/sysdep.h
	(INTERNAL_VSYSCALL_CALL): Remove.
	* sysdeps/unix/sysv/linux/mips/mips64/n32/sysdep.h
	(INTERNAL_VSYSCALL_CALL): Likewise.
	* sysdeps/unix/sysv/linux/mips/mips64/n64/sysdep.h
	(INTERNAL_VSYSCALL_CALL): Likewise.
	* sysdeps/unix/sysv/linux/mips/sysdep.h (INTERNAL_VSYSCALL_CALL):
	New macro.