Move both out of <compat/linux/linux_ioctl.h> and into
<machine/../linux/linux_ioctl.h> and <machine/../linux/linux_termbits.h>,
following the lead of linux_emul_md.h. Every architecture linuxulator
currently supports uses the asm-generic values, so the new per-arch
headers either spell out the generic encoding or just include the common
termbits set, and nothing changes for them.
While here, move the termio structures from linux_ioctl.c up to
linux_ioctl.h, next to the constants that size them.
No functional change intended.