MIPS: vdso: Utilize __pa() for gic_pfn

The GIC user offset is mapped into every process' virtual address and is
therefore part of the hot-path of arch_setup_additional_pages(). Utilize
__pa() such that we are more optimal even when CONFIG_DEBUG_VIRTUAL is
enabled, and while at it utilize PFN_DOWN() instead of open-coding the
right shift by PAGE_SHIFT.
Reported-by: Greg Ungerer <gerg@kernel.org>
Suggested-by: Serge Semin <fancer.lancer@gmail.com>
Fixes: dfad83cb ("MIPS: Add support for CONFIG_DEBUG_VIRTUAL")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Greg Ungerer <gerg@kernel.org>
Tested-by: Greg Ungerer <gerg@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/kernel/vdso.c

@@ -159,7 +159,7 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 	/* Map GIC user page. */
 	if (gic_size) {
 		gic_base = (unsigned long)mips_gic_base + MIPS_GIC_USER_OFS;
-		gic_pfn = virt_to_phys((void *)gic_base) >> PAGE_SHIFT;
+		gic_pfn = PFN_DOWN(__pa(gic_base));
 
 		ret = io_remap_pfn_range(vma, base, gic_pfn, gic_size,
 					 pgprot_noncached(vma->vm_page_prot));