tools: termios_linux.h: Fix compilation on non-glibc systems

tools: termios_linux.h: Fix compilation on non-glibc systems

TCGETS2 is defined in header file asm/ioctls.h provided by linux kernel.
On glib systems it is automatically included by some other glibc include
header file and therefore TCGETS2 is present in termios_linux.h when
linux kernel provides it.

On non-glibc systems (e.g. musl) asm/ioctls.h is not automatically included
which results in the strange error that BOTHER is supported, TCGETS2 not
defined and struct termios does not provide c_ispeed member.

    tools/kwboot.c: In function 'kwboot_tty_change_baudrate':
    tools/kwboot.c:662:6: error: 'struct termios' has no member named 'c_ospeed'
      662 |   tio.c_ospeed = tio.c_ispeed = baudrate;
          |      ^

Fix this issue by explicitly including asm/ioctls.h file which provides
TCGETS2 macro (if supported on selected architecture) to not depending on
glibc auto-include behavior and because termios_linux.h requires it.

With this change it is possible compile kwboot with musl libc.

Reported-by: Michal Vasilek <michal.vasilek@nic.cz>
Signed-off-by: Pali Rohár <pali@kernel.org>