soc: change default CSR bus data-width to 32.

A CSR bus data-width of 32 has been validated on very various design and is
now recommended. It provides better performance without impacting resource
usage (even in iCE40).

CHANGES

@@ -27,6 +27,7 @@
 	--------------------------
 	- BIOS: commands have been renamed/reorganized.
 	- LiteDRAM: rdcmdphase/wrcmdphase no longer exposed.
+	- CSR: change default csr_data_width from 8 to 32.
 
 [> 2020.08, planned for July 2020
 ---------------------------------

litex/soc/doc/csr.py

@@ -63,7 +63,7 @@ def __init__(self, name, address,
             f.description = self.trim(f.description)
 
 class DocumentedCSRRegion:
-    def __init__(self, name, region, module=None, submodules=[], csr_data_width=8):
+    def __init__(self, name, region, module=None, submodules=[], csr_data_width=32):
         self.name            = name
         self.origin          = region.origin
         self.busword         = region.busword

litex/soc/integration/soc_core.py

@@ -80,7 +80,7 @@ def __init__(self, platform, clk_freq,
         integrated_main_ram_size = 0,
         integrated_main_ram_init = [],
         # CSR parameters
-        csr_data_width           = 8,
+        csr_data_width           = 32,
         csr_address_width        = 14,
         csr_paging               = 0x800,
         csr_ordering             = "big",
@@ -282,7 +282,7 @@ def soc_core_args(parser):
                         help="size/enable the integrated main RAM")
     # CSR parameters
     parser.add_argument("--csr-data-width", default=None, type=auto_int,
-                        help="CSR bus data-width (8 or 32, default=8)")
+                        help="CSR bus data-width (8 or 32, default=32)")
     parser.add_argument("--csr-address-width", default=14, type=auto_int,
                         help="CSR bus address-width")
     parser.add_argument("--csr-paging", default=0x800, type=auto_int,