mor1kx: Enable rotate, sign extend under linux, new fpu extension

My thought is that if we are running linux the FPGA should be able to
handle these extra instruction's footprint.  Also, since we are running
on linux there may be any kind of software running on the CPU, so allow
handling these instructions.

FPU is added bia a new +fpu extension.

But really, I am running GLIBC tests and they run faster with this
enabled.

litex/soc/cores/cpu/mor1kx/core.py

@@ -15,7 +15,7 @@
 from litex.soc.interconnect import wishbone
 from litex.soc.cores.cpu import CPU
 
-CPU_VARIANTS = ["standard", "linux"]
+CPU_VARIANTS = ["standard", "standard+fpu", "linux", "linux+fpu"]
 
 
 class MOR1KX(CPU):
@@ -51,6 +51,11 @@ def gcc_flags(self):
         flags =  "-mhard-mul "
         flags += "-mhard-div "
         flags += "-D__mor1kx__ "
+
+        if "linux" in self.variant:
+            flags += "-mror "
+            flags += "-msext "
+
         return flags
 
     @property
@@ -77,7 +82,7 @@ def __init__(self, platform, variant="standard"):
         self.memory_buses = []
 
 
-        if variant == "linux":
+        if "linux" in variant:
             self.mem_map = self.mem_map_linux
 
         # # #
@@ -107,14 +112,21 @@ def __init__(self, platform, variant="standard"):
             p_DBUS_WB_TYPE              = "B3_REGISTERED_FEEDBACK",
         )
 
-        if variant == "linux":
+        if "fpu" in variant:
+            cpu_args.update(
+                p_FEATURE_FPU = "ENABLED",
+            )
+
+        if "linux" in variant:
             cpu_args.update(
                 # Linux needs the memory management units.
                 p_FEATURE_IMMU  = "ENABLED",
                 p_FEATURE_DMMU  = "ENABLED",
                 # FIXME: Currently we need the or1k timer when we should be
                 # using the litex timer.
                 p_FEATURE_TIMER = "ENABLED",
+                p_FEATURE_ROR = "ENABLED",
+                p_FEATURE_EXT = "ENABLED",
             )
             # FIXME: Check if these are needed?
             use_defaults = (