arm64: Use generic kernel_execve() implementation

This patch enables CONFIG_GENERIC_KERNEL_EXECVE on arm64 and removes the
arm64-specific implementation of kernel_execve().

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 4077b71..75b212d 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -6,6 +6,7 @@
 	select GENERIC_IOMAP
 	select GENERIC_IRQ_PROBE
 	select GENERIC_IRQ_SHOW
+	select GENERIC_KERNEL_EXECVE
 	select GENERIC_KERNEL_THREAD
 	select GENERIC_SMP_IDLE_THREAD
 	select GENERIC_TIME_VSYSCALL