Hexagon: use generic sys_fork, sys_vfork, and sys_clone

Signed-off-by: Richard Kuo <rkuo@codeaurora.org>

arch/hexagon/Kconfig

@@ -30,6 +30,8 @@ config HEXAGON
 	select GENERIC_CLOCKEVENTS_BROADCAST
 	select MODULES_USE_ELF_RELA
 	select GENERIC_CPU_DEVICES
+	select GENERIC_KERNEL_THREAD
+	select GENERIC_KERNEL_EXECVE
 	---help---
 	  Qualcomm Hexagon is a processor architecture designed for high
 	  performance and low power across a wide variety of applications.

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

@@ -27,6 +27,9 @@
  */
 
 #define sys_mmap2 sys_mmap_pgoff
+#define __ARCH_WANT_SYS_EXECVE
 #define __ARCH_WANT_SYS_CLONE
+#define __ARCH_WANT_SYS_VFORK
+#define __ARCH_WANT_SYS_FORK
 
 #include <asm-generic/unistd.h>