termios: Consolidate termios.h

This patch consolidates the Linux termios.h by removing the arch-specific
one.

No semantic change is expected, checked on a build against x86_64-linux-gnu,
alpha-linux-gnu, mips64-linux-gnu, and sparc64-linux-gnu.

	* sysdeps/unix/sysv/linux/Makefile (sysdep_headers): Add
	bits/termios-misc.h.
	* sysdeps/unix/sysv/linux/alpha/bits/termios.h: Remove file.
	* sysdeps/unix/sysv/linux/mips/bits/termios.h: Likewise.
	* sysdeps/unix/sysv/linux/sparc/bits/termios.h: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/bits/termios.h: Likewise.
	* sysdeps/unix/sysv/linux/bits/termios-misc.h: New file.
	* sysdeps/unix/sysv/linux/bits/termios.h: Include termios-misc.h.