x86/boot: Fix PVH boot following the start of the MBI->BI conversion

pvh_init() sets up the mbi pointer, but leaves mbi_p at 0.  This isn't
compatbile with multiboot_fill_boot_info() starting from the physical address,
in order to remove the use of the mbi pointer.

Fixes: 038826b61e ("x86/boot: move x86 boot module counting into a new boot_info struct")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Daniel P. Smith <dpsmith@apertussolutions.com>

xen/arch/x86/setup.c

@@ -1048,6 +1048,7 @@ void asmlinkage __init noreturn __start_xen(unsigned long mbi_p)
     {
         ASSERT(mbi_p == 0);
         pvh_init(&mbi, &mod);
+        mbi_p = __pa(mbi);
     }
     else
     {