target-i386: x86_cpu_get_phys_page_debug(): support 1GB page translation

target-i386: x86_cpu_get_phys_page_debug(): support 1GB page translation

Linux guests, when using more than 4GB of RAM, may end up using 1GB pages
to store (kernel) data. When this happens, we're unable to debug a running
Linux kernel with GDB:

(gdb) p node_data[0]->node_id
Cannot access memory at address 0xffff88013fffd3a0
(gdb)

GDB returns this error because x86_cpu_get_phys_page_debug() doesn't support
translating 1GB pages in IA-32e paging mode and returns an error to GDB.

This commit adds support for 1GB page translation for IA32e paging.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>