ARCv2: Support IO Coherency and permutations involving L1 and L2 caches

In case of ARCv2 CPU there're could be following configurations
that affect cache handling for data exchanged with peripherals
via DMA:
 [1] Only L1 cache exists
 [2] Both L1 and L2 exist, but no IO coherency unit
 [3] L1, L2 caches and IO coherency unit exist

Current implementation takes care of [1] and [2].
Moreover support of [2] is implemented with run-time check
for SLC existence which is not super optimal.

This patch introduces support of [3] and rework of DMA ops
usage. Instead of doing run-time check every time a particular
DMA op is executed we'll have 3 different implementations of
DMA ops and select appropriate one during init.

As for IOC support for it we need:
 [a] Implement empty DMA ops because IOC takes care of cache
     coherency with DMAed data
 [b] Route dma_alloc_coherent() via dma_alloc_noncoherent()
     This is required to make IOC work in first place and also
     serves as optimization as LD/ST to coherent buffers can be
     srviced from caches w/o going all the way to memory

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
[vgupta:
  -Added some comments about IOC gains
  -Marked dma ops as static,
  -Massaged changelog a bit]
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/include/asm/cache.h

@@ -53,6 +53,8 @@ extern void arc_cache_init(void);
 extern char *arc_cache_mumbojumbo(int cpu_id, char *buf, int len);
 extern void read_decode_cache_bcr(void);
 
+extern int ioc_exists;
+
 #endif	/* !__ASSEMBLY__ */
 
 /* Instruction cache related Auxiliary registers */
@@ -94,4 +96,10 @@ extern void read_decode_cache_bcr(void);
 #define SLC_CTRL_BUSY		0x100
 #define SLC_CTRL_RGN_OP_INV	0x200
 
+/* IO coherency related Auxiliary registers */
+#define ARC_REG_IO_COH_ENABLE	0x500
+#define ARC_REG_IO_COH_PARTIAL	0x501
+#define ARC_REG_IO_COH_AP0_BASE	0x508
+#define ARC_REG_IO_COH_AP0_SIZE	0x509
+
 #endif /* _ASM_CACHE_H */