x86/entry/32: Rename 32-bit specific syscalls

Rename the syscalls that only exist for 32-bit from x86_* to ia32_* to make it
clear they are for 32-bit only.  Also rename the functions to match the syscall
name.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Link: https://lkml.kernel.org/r/20200313195144.164260-15-brgerst@gmail.com