rename target_phy_addr_t to hwaddr to match upstream.

Upstream got rid of the target_phys_addr_t and replaced it with 'hwaddr',
so do the corresponding rename here. Note that:

- This also renames <exec/targphys.h> to <exec/hwaddr.h>

- Upstream always deins hwaddr as a 64-bit type, while the size of
  our own hwaddr is still controlled by TARGET_PHYS_ADDR_BITS, and
  will be 32 for now.

  A future patch will change the type definition to fully match
  upstream, but it is more risky / requires more cleanups. It's
  simply cleaner / simpler to put the related work in a separate
  patch, given the large number of sources touched by the
  current change.

Change-Id: Iee30869a57798c12109b6a23570b166232bb9244
diff --git a/hw/pci-host/piix.c b/hw/pci-host/piix.c
index 78bb72f..43ee738 100644
--- a/hw/pci-host/piix.c
+++ b/hw/pci-host/piix.c
@@ -55,7 +55,7 @@
     return (irq_num + slot_addend) & 3;
 }
 
-static target_phys_addr_t isa_page_descs[384 / 4];
+static hwaddr isa_page_descs[384 / 4];
 static uint8_t smm_enabled;
 static int pci_irq_levels[4];