Loader: Make the load address mask be a parameter of the system rather than a constant.

This allows one two different OS requirements for the same ISA to be handled.
Some OSes are compiled for a virtual address and need to be loaded into physical
memory that starts at address 0, while other bare metal tools generate
images that start at address 0.

src/arch/mips/MipsSystem.py

@@ -41,6 +41,7 @@ class MipsSystem(System):
     hex_file_name = Param.String("test.hex","hex file that contains [address,data] pairs")
     system_type = Param.UInt64("Type of system we are emulating")
     system_rev = Param.UInt64("Revision of system we are emulating")
+    load_addr_mask = 0xffffffffff
 
 if buildEnv['FULL_SYSTEM']:
     class LinuxMipsSystem(MipsSystem):