Move the arm64 sigcode to .rodata

The kernel doesn't execute this code, it's only ever copied to
userspace. Move it to .rodata as we don't need to modify it.

Sponsored by:	Arm Ltd
Differential Revision:	https://reviews.freebsd.org/D39399

sys/arm64/arm64/locore.S

@@ -918,8 +918,10 @@ pagetable_end:
 el2_pagetable:
 	.space	PAGE_SIZE
 
-.text
-EENTRY(aarch32_sigcode)
+	.section .rodata, "a", %progbits
+	.globl	aarch32_sigcode
+	.align 2
+aarch32_sigcode:
 	.word 0xe1a0000d	// mov r0, sp
 	.word 0xe2800040	// add r0, r0, #SIGF_UC
 	.word 0xe59f700c	// ldr r7, [pc, #12]
@@ -927,10 +929,10 @@ EENTRY(aarch32_sigcode)
 	.word 0xe59f7008	// ldr r7, [pc, #8]
 	.word 0xef000000	// swi #0
 	.word 0xeafffffa	// b . - 16
-EEND(aarch32_sigcode)
 	.word SYS_sigreturn
 	.word SYS_exit
 	.align	3
+	.size aarch32_sigcode, . - aarch32_sigcode
 aarch32_esigcode:
 	.data
 	.global sz_aarch32_sigcode

sys/arm64/arm64/sigtramp.S

@@ -30,7 +30,10 @@
 #include <sys/syscall.h>
 #include <machine/asm.h>
 
-ENTRY(sigcode)
+	.section .rodata, "a", %progbits
+	.globl	sigcode
+	.align 2
+sigcode:
 	blr	x8
 	mov	x0, sp
 	add	x0, x0, #SF_UC
@@ -44,9 +47,9 @@ ENTRY(sigcode)
 	svc	0
 
 	b	1b
-END(sigcode)
 	/* This may be copied to the stack, keep it 16-byte aligned */
 	.align	3
+	.size sigcode, . - sigcode
 esigcode:
 
 	.data