syscon: Add flag to indicate the timebase frequency

This adds a flag (currently not set) to indicate that the core is using
the architected timebase frequency of 512Mhz. When not set, the core is
using the proc frequency for the timebase.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

include/microwatt_soc.h

@@ -39,6 +39,7 @@
 #define   SYS_REG_INFO_HAS_LITEETH 		(1ull << 4)
 #define   SYS_REG_INFO_HAS_LARGE_SYSCON	        (1ull << 5)
 #define   SYS_REG_INFO_HAS_UART1 		(1ull << 6)
+#define   SYS_REG_INFO_HAS_ARTB                 (1ull << 7)
 #define SYS_REG_BRAMINFO		0x10
 #define   SYS_REG_BRAMINFO_SIZE_MASK		0xfffffffffffffull
 #define SYS_REG_DRAMINFO		0x18

syscon.vhdl

@@ -64,6 +64,7 @@ architecture behaviour of syscon is
     constant SYS_REG_INFO_HAS_LETH    : integer := 4;  -- Has LiteEth ethernet
     constant SYS_REG_INFO_HAS_LSYS    : integer := 5;  -- Has 6-bit address syscon
     constant SYS_REG_INFO_HAS_URT1    : integer := 6;  -- Has second UART
+    constant SYS_REG_INFO_HAS_ARTB    : integer := 7;  -- Has architected TB frequency
 
     -- BRAMINFO contains the BRAM size in the bottom 52 bits
     -- DRAMINFO contains the DRAM size if any in the bottom 52 bits