termios: Consolidate termios c_cc symbolic constants

This patch consolidates the termios symbolic constants used as subscript
for the array c_cc on its own header.  The Linux generic implementation
values match the kernel UAPI and each architecture with deviate values
have their own implementation (in this case alpha, mips64, sparc64, and
powerpc).

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 (sysdeps_headers): Add
	termios-cc.h.
	* sysdeps/unix/sysv/linux/bits/termios-c_cc.h: Likewise.
	* sysdeps/unix/sysv/linux/alpha/bits/termios-c_cc.h: New file.
	* sysdeps/unix/sysv/linux/mips/bits/termios-c_cc.h: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/bits/termios-c_cc.h: Likewise.
	* sysdeps/unix/sysv/linux/sparc/bits/termios-c_cc.h: Likewise.
	* sysdeps/unix/sysv/linux/bits/termios.h (VINTR, VQUIT, VERASE,
	VKILL, VEOF, VTIME, VMIN, VSWTC, VSTART, VSTOP, VSUSP, VEOL,
	VREPRINT, VDISCARD, VWERASE, VLNEXT, VEOLF2): Move to termios-cc.h.
	* sysdeps/unix/sysv/linux/alpha/bits/termios.h: Likewise.
	* sysdeps/unix/sysv/linux/mips/bits/termios.h: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/bits/termios.h: Likewise.
	* sysdeps/unix/sysv/linux/sparc/bits/termios.h: Likewise.