[i386] Add dump_regs() debug call

Use as "call dump_regs" from any real-mode code within .text16.
Should preserve all registers and flags.

src/arch/i386/core/dumpregs.c

@@ -0,0 +1,23 @@
+#include <stdio.h>
+#include <realmode.h>
+
+void __cdecl _dump_regs ( struct i386_all_regs *ix86 ) {
+
+	__asm__ __volatile__ (
+		TEXT16_CODE ( ".globl dump_regs\n\t"
+			      "\ndump_regs:\n\t"
+			      "pushl $_dump_regs\n\t"
+			      "pushw %%cs\n\t"
+			      "call prot_call\n\t"
+			      "addr32 leal 4(%%esp), %%esp\n\t"
+			      "ret\n\t" ) : : );
+
+	printf ( "EAX=%08lx EBX=%08lx ECX=%08lx EDX=%08lx\n"
+		 "ESI=%08lx EDI=%08lx EBP=%08lx ESP=%08lx\n"
+		 "CS=%04x SS=%04x DS=%04x ES=%04x FS=%04x GS=%04x\n",
+		 ix86->regs.eax, ix86->regs.ebx, ix86->regs.ecx,
+		 ix86->regs.edx, ix86->regs.esi, ix86->regs.edi,
+		 ix86->regs.ebp, ix86->regs.esp,
+		 ix86->segs.cs, ix86->segs.ss, ix86->segs.ds,
+		 ix86->segs.es, ix86->segs.fs, ix86->segs.gs );
+}