examples: fix building on arm64

Commit f9886bc60f ("Added arm64 assembly for examples/api crt0") tried to
add arm64 support to the examples but crt0.S does not even build for
qemu_arm64_defconfig with CONFIG_API=y, CONFIG_EXAMPLES=y:

    examples/api/crt0.S: Assembler messages:
    examples/api/crt0.S:32: Error:
        expected a register at operand 1 -- `ldr ip,=search_hint'
    examples/api/crt0.S:33: Error:
        unexpected register type at operand 1 -- `str sp,[ip]'
    make[2]: *** [scripts/Makefile.build:292: examples/api/crt0.o] Error 1

Do not define _start twice.
Use valid register names.
Move syscall_ptr and search_hint to the data section to avoid an invalid
relocation.

Fixes: f9886bc60f ("Added arm64 assembly for examples/api crt0")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

examples/api/crt0.S

@@ -24,7 +24,7 @@ syscall:
 	mtctr	%r11
 	bctr
 
-#elif defined(CONFIG_ARM)
+#elif defined(CONFIG_ARM) && !defined(CONFIG_ARM64)
 
 	.text
 	.globl _start
@@ -33,27 +33,28 @@ _start:
 	str	sp, [ip]
 	b	main
 
-#elif defined(CONFIG_ARM64)
-
-              .text
-              .globl _start
-_start:
-              ldr           ip0, =search_hint
-              str           sp_el2, [ip0]
-              b             main
-
-
-              .globl syscall
-syscall:
-              ldr           ip0, =syscall_ptr
-              ldr           pc_el2, [ip0]
-
 
 	.globl syscall
 syscall:
 	ldr	ip, =syscall_ptr
 	ldr	pc, [ip]
 
+#elif defined(CONFIG_ARM64)
+
+	.text
+	.globl _start
+_start:
+	ldr	x17, =search_hint
+	mov	x16, sp
+	str	x16, [x17]
+	b	main
+
+	.globl syscall
+syscall:
+	ldr	x16, =syscall_ptr
+	ldr	x16, [x16]
+	br	x16
+
 #elif defined(CONFIG_MIPS)
 #include <asm/asm.h>
 	.text
@@ -83,6 +84,8 @@ return_addr:
 #error No support for this arch!
 #endif
 
+.section .data
+
 	.globl syscall_ptr
 syscall_ptr:
 	.align	8
@@ -90,4 +93,4 @@ syscall_ptr:
 
 	.globl search_hint
 search_hint:
-	.long   0
+	.long	0