alpha: update syscall macro definitions

alpha: update syscall macro definitions

Other architectures commonly use __NR_umount2 for sys_umount,
only ia64 and alpha use __NR_umount here. In order to synchronize
the generated tables, use umount2 like everyone else, and add back
the old name from asm/unistd.h for compatibility.

For shmat, alpha uses the osf_shmat name, we can do the same thing
here, which means we don't have to add an entry in the __IGNORE
list now that shmat is mandatory everywhere

alarm, creat, pause, time, and utime are optional everywhere
these days, no need to list them here any more.

I considered also adding the regular versions of the get*id system
calls that have different names and calling conventions on alpha,
which would further help unify the syscall ABI, but for now
I decided against that.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>