riscv: Use new ctors _entry func as entry point

Signed-off-by: Callum Farmer <gmbr3@opensuse.org>

gnuefi/crt0-efi-riscv64.S

@@ -130,7 +130,7 @@ _start:
 	bne		a0, zero, 0f
 	ld		a1, 8(sp)
 	ld		a0, 0(sp)
-	call		efi_main
+	call		_entry
 	ld		ra, 16(sp)
 0:	addi		sp, sp, 24
 	ret