[ARM] nommu: adjust headers for !MMU ARM systems

Majorily based on Hyok Choi's patches, this fixes up the asm-arm
header files for mmuless systems.  Over and above Hyok's patches:

- nommu.h merged into mmu.h (it's only a structure)
- nommu_context.h is essentially the same as mmu_context.h, but
  without the MM switching code.

so there's no point having separate files.  Also, in memory.h,
there's no point #ifndef'ing PHYS_OFFSET and END_MEM - both
CONFIG_DRAM_BASE and CONFIG_DRAM_SIZE will always be set by the
configuration scripts.

Other files have minor formatting changes, but are essentially
the same.  Hyok's original patches were signed off thusly:

  Signed-off-by: Hyok S. Choi <hyok.choi@samsung.com>

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

include/asm-arm/pgtable.h

@@ -11,9 +11,15 @@
 #define _ASMARM_PGTABLE_H
 
 #include <asm-generic/4level-fixup.h>
+#include <asm/proc-fns.h>
+
+#ifndef CONFIG_MMU
+
+#include "pgtable-nommu.h"
+
+#else
 
 #include <asm/memory.h>
-#include <asm/proc-fns.h>
 #include <asm/arch/vmalloc.h>
 
 /*
@@ -378,4 +384,6 @@ extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
 
 #endif /* !__ASSEMBLY__ */
 
+#endif /* CONFIG_MMU */
+
 #endif /* _ASMARM_PGTABLE_H */