mfd: intel-lpss: Use devm_ioremap_uc for MMIO

Some BIOS erroneously specifies write-combining BAR for intel-lpss-pci
in MTRR. This will cause the system to hang during boot. If possible,
this bug could be corrected with a firmware update.

This patch use devm_ioremap_uc to overwrite/ignore the MTRR settings
by forcing the use of strongly uncachable pages for intel-lpss.

The BIOS bug is present on Dell XPS 13 7390 2-in-1:

[ 0.001734] 5 base 4000000000 mask 6000000000 write-combining

4000000000-7fffffffff : PCI Bus 0000:00
4000000000-400fffffff : 0000:00:02.0 (i915)
4010000000-4010000fff : 0000:00:15.0 (intel-lpss-pci)

Link: https://bugzilla.kernel.org/show_bug.cgi?id=203485
Cc: <[e-mail]> # v4.19+
Tested-by: AceLan Kao <[e-mail]>
Signed-off-by: Tuowen Zhao <[e-mail]>
Acked-by: Mika Westerberg <[e-mail]>
Acked-by: Andy Shevchenko <[e-mail]>
Tested-by: Roman Gilg <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

drivers/mfd/intel-lpss.c

···
 	if (!lpss)
 		return -ENOMEM;
 
-	lpss->priv = devm_ioremap(dev, info->mem->start + LPSS_PRIV_OFFSET,
+	lpss->priv = devm_ioremap_uc(dev, info->mem->start + LPSS_PRIV_OFFSET,
 				  LPSS_PRIV_SIZE);
 	if (!lpss->priv)
 		return -ENOMEM;