xen/pt: add a few PCI config space field descriptions

Since the next patch will turn all not explicitly described fields
read-only by default, those fields that have guest writable bits need
to be given explicit descriptors.

This is a preparatory patch for XSA-131.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
Notes:
- blindly allowing all VPD reads may still be a problem (out of bounds
  addresses aren't allowed, but the spec doesn't say what the effect
  would be) ==> also an issue in pciback?
- Vendor Specific cap regs aren't in the table (will become r/o by
  default with this change)
- many PCIe cap regs aren't in the table (will again become r/o)
- same for PM cap regs at offsets 6 and 7

--- a/hw/xen_pt_config_init.c
+++ b/hw/xen_pt_config_init.c
@@ -756,6 +756,15 @@ static XenPTRegInfo xen_pt_emu_reg_vpd[]
         .u.b.write  = xen_pt_byte_reg_write,
     },
     {
+        .offset     = PCI_VPD_ADDR,
+        .size       = 2,
+        .ro_mask    = 0x0003,
+        .emu_mask   = 0x0003,
+        .init       = xen_pt_common_reg_init,
+        .u.w.read   = xen_pt_word_reg_read,
+        .u.w.write  = xen_pt_word_reg_write,
+    },
+    {
         .size = 0,
     },
 };
@@ -891,6 +900,16 @@ static XenPTRegInfo xen_pt_emu_reg_pcie[
         .u.w.read   = xen_pt_word_reg_read,
         .u.w.write  = xen_pt_word_reg_write,
     },
+    /* Device Status reg */
+    {
+        .offset     = PCI_EXP_DEVSTA,
+        .size       = 2,
+        .res_mask   = 0xFFC0,
+        .ro_mask    = 0x0030,
+        .init       = xen_pt_common_reg_init,
+        .u.w.read   = xen_pt_word_reg_read,
+        .u.w.write  = xen_pt_word_reg_write,
+    },
     /* Link Control reg */
     {
         .offset     = PCI_EXP_LNKCTL,
@@ -902,6 +921,15 @@ static XenPTRegInfo xen_pt_emu_reg_pcie[
         .u.w.read   = xen_pt_word_reg_read,
         .u.w.write  = xen_pt_word_reg_write,
     },
+    /* Link Status reg */
+    {
+        .offset     = PCI_EXP_LNKSTA,
+        .size       = 2,
+        .ro_mask    = 0x3FFF,
+        .init       = xen_pt_common_reg_init,
+        .u.w.read   = xen_pt_word_reg_read,
+        .u.w.write  = xen_pt_word_reg_write,
+    },
     /* Device Control 2 reg */
     {
         .offset     = 0x28,