sh: Provide a sane valid_phys_addr_range() to prevent TLB reset with PMB.

With the PMB enabled, only P1SEG and up are covered by the PMB mappings,
meaning that situations where out-of-bounds physical addresses are read
from will lead to TLB reset after the PMB miss, allowing for use cases
like dd if=/dev/mem to reset the TLB.

Fix this up to make sure the reference is between __MEMORY_START (phys)
and __pa(high_memory). This is coherent across all variants of sh/sh64
with and without MMU, though the PMB bug itself is only applicable to
SH-4A parts.

Reported-by: Hideo Saito <saito@densan.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/include/asm/io.h

@@ -293,6 +293,10 @@ __ioremap_mode(unsigned long offset, unsigned long size, unsigned long flags)
  */
 #define xlate_dev_kmem_ptr(p)	p
 
+#define ARCH_HAS_VALID_PHYS_ADDR_RANGE
+int valid_phys_addr_range(unsigned long addr, size_t size);
+int valid_mmap_phys_addr_range(unsigned long pfn, size_t size);
+
 #endif /* __KERNEL__ */
 
 #endif /* __ASM_SH_IO_H */