alpha: add generic get{eg,eu,g,p,u,pp}id() syscalls

Alpha has traditionally followed the OSF1 calling conventions
here, with its getxpid, getxuid, getxgid system calls returning
two different values in separate registers.

Following what glibc has done here, we can define getpid,
getuid and getgid to be aliases for getxpid, getxuid and getxgid
respectively, and add new system call numbers for getppid, geteuid
and getegid.

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

arch/alpha/kernel/syscalls/syscall.tbl

@@ -458,3 +458,6 @@
 527	common	rseq				sys_rseq
 528	common	statfs64			sys_statfs64
 529	common	fstatfs64			sys_fstatfs64
+530	common	getegid				sys_getegid
+531	common	geteuid				sys_geteuid
+532	common	getppid				sys_getppid