arm64: set MAX_MEMBLOCK_ADDR according to linear region size

The linear region size of a 39-bit VA kernel is only 256 GB, which
may be insufficient to cover all of system RAM, even on platforms
that have much less than 256 GB of memory but which is laid out
very sparsely.

So make sure we clip the memory we will not be able to map before
installing it into the memblock memory table, by setting
MAX_MEMBLOCK_ADDR accordingly.
Reviewed-by: NCatalin Marinas <catalin.marinas@arm.com>
Tested-by: NStuart Yoder <stuart.yoder@freescale.com>
Signed-off-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm64/include/asm/memory.h

@@ -113,6 +113,14 @@ extern phys_addr_t		memstart_addr;
 /* PHYS_OFFSET - the physical address of the start of memory. */
 #define PHYS_OFFSET		({ memstart_addr; })
 
+/*
+ * The maximum physical address that the linear direct mapping
+ * of system RAM can cover. (PAGE_OFFSET can be interpreted as
+ * a 2's complement signed quantity and negated to derive the
+ * maximum size of the linear mapping.)
+ */
+#define MAX_MEMBLOCK_ADDR	({ memstart_addr - PAGE_OFFSET - 1; })
+
 /*
  * PFNs are used to describe any physical page; this means
  * PFN 0 == physical address 0.