alpha: Wire up all missing implemented syscalls

And still left the missing unimplemented syscalls as warnings. The
related warnings for missing implemented syscalls:

CALL scripts/checksyscalls.sh
<stdin>:1241:2: warning: #warning syscall getrandom not implemented [-Wcpp]
<stdin>:1244:2: warning: #warning syscall memfd_create not implemented [-Wcpp]
<stdin>:1250:2: warning: #warning syscall execveat not implemented [-Wcpp]

Signed-off-by: Chen Gang <[e-mail]>
Signed-off-by: Matt Turner <[e-mail]>

arch/alpha/include/asm/unistd.h

···
 
 #include <uapi/asm/unistd.h>
 
-#define NR_SYSCALLS			511
+#define NR_SYSCALLS			514
 
 #define __ARCH_WANT_OLD_READDIR
 #define __ARCH_WANT_STAT64

arch/alpha/include/uapi/asm/unistd.h

···
 #define __NR_sched_setattr		508
 #define __NR_sched_getattr		509
 #define __NR_renameat2			510
+#define __NR_getrandom			511
+#define __NR_memfd_create		512
+#define __NR_execveat			513
 
 #endif /* _UAPI_ALPHA_UNISTD_H */

arch/alpha/kernel/systbls.S

···
 	.quad sys_sched_setattr
 	.quad sys_sched_getattr
 	.quad sys_renameat2			/* 510 */
+	.quad sys_getrandom
+	.quad sys_memfd_create
+	.quad sys_execveat
 
 	.size sys_call_table, . - sys_call_table
 	.type sys_call_table, @object