platform/x86: intel_pmc_core: Do not ioremap RAM

On a Xen-based PVH virtual machine with more than 4 GiB of RAM,
intel_pmc_core fails initialization with the following warning message
from the kernel, indicating that the driver is attempting to ioremap
RAM:

  ioremap on RAM at 0x00000000fe000000 - 0x00000000fe001fff
  WARNING: CPU: 1 PID: 434 at arch/x86/mm/ioremap.c:186 __ioremap_caller.constprop.0+0x2aa/0x2c0
...
  Call Trace:
   ? pmc_core_probe+0x87/0x2d0 [intel_pmc_core]
   pmc_core_probe+0x87/0x2d0 [intel_pmc_core]

This issue appears to manifest itself because of the following fallback
mechanism in the driver:

	if (lpit_read_residency_count_address(&slp_s0_addr))
		pmcdev->base_addr = PMC_BASE_ADDR_DEFAULT;

The validity of address PMC_BASE_ADDR_DEFAULT (i.e., 0xFE000000) is not
verified by the driver, which is what this patch introduces. With this
patch, if address PMC_BASE_ADDR_DEFAULT is in RAM, then the driver will
not attempt to ioremap the aforementioned address.
Signed-off-by: M. Vefa Bicakci <m.v.b@runbox.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/platform/x86/intel_pmc_core.c

@@ -878,10 +878,14 @@ static int pmc_core_probe(struct platform_device *pdev)
 	if (pmcdev->map == &spt_reg_map && !pci_dev_present(pmc_pci_ids))
 		pmcdev->map = &cnp_reg_map;
 
-	if (lpit_read_residency_count_address(&slp_s0_addr))
+	if (lpit_read_residency_count_address(&slp_s0_addr)) {
 		pmcdev->base_addr = PMC_BASE_ADDR_DEFAULT;
-	else
+
+		if (page_is_ram(PHYS_PFN(pmcdev->base_addr)))
+			return -ENODEV;
+	} else {
 		pmcdev->base_addr = slp_s0_addr - pmcdev->map->slp_s0_offset;
+	}
 
 	pmcdev->regbase = ioremap(pmcdev->base_addr,
 				  pmcdev->map->regmap_length);