[prefix] Standardise calls to prot_call()

Use the standard "pushl $function ; pushw %cs ; call prot_call"
sequence everywhere that prot_call() is used.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/x86/prefix/libprefix.S

 	movw	%ax, (init_librm_vector+2)
 	lcall	*init_librm_vector
 
+	/* Prepare for return to .prefix segment */
+	pushw	%cs
+
+	/* Jump to .text16 segment */
+	pushw	%ax
+	pushw	$1f
+	lret
+	.section ".text16.install_prealloc", "ax", @progbits
+1:
 	/* Inhibit INT 15,e820 and INT 15,e801 if applicable */
 	testl	%ebp, %ebp
 	jnz	1f
 	 * ready for the copy to the new location.
 	 */
 	progress "  relocate\n"
-	movw	%ax, (prot_call_vector+2)
 	pushl	$relocate
-	lcall	*prot_call_vector
+	pushw	%cs
+	call	prot_call
 
+	/* Jump back to .prefix segment */
+	pushw	$1f
+	lret
+	.section ".prefix.install_prealloc", "awx", @progbits
+1:
 	/* Copy code to new location */
 	progress "  copy\n"
 	pushl	%edi
 	.word init_librm
 	.word 0
 	.size init_librm_vector, . - init_librm_vector
-prot_call_vector:
-	.word prot_call
-	.word 0
-	.size prot_call_vector, . - prot_call_vector
 #endif
 close_payload_vector:
 	.word close_payload

src/arch/x86/prefix/undiloader.S

 	pushw	%ds
 	pushw	%es
 	pushw	%bx
+
 	/* ROM segment address to %ds */
 	pushw	%cs
 	popw	%ds
+
 	/* UNDI loader parameter structure address into %es:%di */
 	movw	%sp, %bx
 	movw	%ss:22(%bx), %di
 	movw	%ss:24(%bx), %es
+
 	/* Install to specified real-mode addresses */
 	pushw	%di
 	movw	%es:12(%di), %bx
 	orl	$0xffffffff, %ebp	/* Allow arbitrary relocation */
 	call	install_prealloc
 	popw	%di
+
+	/* Jump to .text16 segment */
+	pushw	%ax
+	pushw	$1f
+	lret
+	.section ".text16", "ax", @progbits
+1:
 	/* Call UNDI loader C code */
 	pushl	$pxe_loader_call
 	pushw	%cs
-	pushw	$1f
-	pushw	%ax
-	pushw	$prot_call
-	lret
+	call	prot_call
+
 1:	/* Restore registers and return */
 	popw	%bx
 	popw	%es
 	popl	%edi
 	popl	%esi
 	lret
-	.size undiloader, . - undiloader