soc/intel/quark: Conditionally define BIT names

Only define BIT names if they are not already defined.

TEST=Build and run on Galileo Gen2

Change-Id: Ief4c4bb7a42a1bb2a7f46f13dc9b8bbb4d233e3c
Signed-off-by: Lee Leahy <leroy.p.leahy@intel.com>
Reviewed-on: https://review.coreboot.org/15002
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

src/soc/intel/quark/include/soc/QuarkNcSocId.h

@@ -24,6 +24,7 @@ Definitions beginning with "N_" are the bit position
 //
 // Define the bits
 //
+#ifndef BIT0
 #define BIT0        0x00000001
 #define BIT1        0x00000002
 #define BIT2        0x00000004
@@ -56,6 +57,7 @@ Definitions beginning with "N_" are the bit position
 #define BIT29       0x20000000
 #define BIT30       0x40000000
 #define BIT31       0x80000000
+#endif
 
 //
 // QNC GMCH Equates