ARM: 7947/1: Make pgtbl macro more robust

The pgtbl macro couldn't handle the specific
(TEXT_OFFSET - PG_DIR_SIZE) value that the combination of
MSM platforms and LPAE created:

head.S:163: Error: invalid constant (203000) after fixup

Regardless of whether this combination of configuration options
will work on currently support platforms at run time, make it
at least assemble properly.
Signed-off-by: NChristopher Covington <cov@codeaurora.org>
Reviewed-by: NStephen Boyd <sboyd@codeaurora.org>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/head.S

@@ -52,7 +52,8 @@
 	.equ	swapper_pg_dir, KERNEL_RAM_VADDR - PG_DIR_SIZE
 
 	.macro	pgtbl, rd, phys
-	add	\rd, \phys, #TEXT_OFFSET - PG_DIR_SIZE
+	add	\rd, \phys, #TEXT_OFFSET
+	sub	\rd, \rd, #PG_DIR_SIZE
 	.endm
 
 /*