alpha: move __IGNORE* entries to non uapi header

All the __IGNORE* entries are resides in the uapi header
file move to non uapi header asm/unistd.h as it is not
used by any user space applications.

It is correct to keep __IGNORE* entry in non uapi header
asm/unistd.h while uapi/asm/unistd.h must hold information
only useful for user space applications.

One of the patch in this patch series will generate uapi
header file. The information which directly used by the
user space application must be present in uapi file.

Signed-off-by: Firoz Khan <firoz.khan@linaro.org>
Signed-off-by: Matt Turner <mattst88@gmail.com>