arch-mips: Replaced `BigEndianByteOrder` in MIPS

The following change removed the `BigEndianByteOrder` enum and replaced
it with `ByteOrder:big`:
https://gem5-review.googlesource.com/c/public/gem5/+/33174

This change was not propogated to `src/arch/mips/isa/decoder.isa` and
`src/arch/mips/isa/formats/mem.isa`, and therefore caused compilation
errors. This caused the Nightly Build to fail:
https://www.mail-archive.com/gem5-dev@gem5.org/msg35900.html

This commit fixes this error.

Change-Id: I3967eb9e9236a7a95318c17ca410b613b8473eed
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/34255
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
diff --git a/src/arch/mips/isa/decoder.isa b/src/arch/mips/isa/decoder.isa
index d35fc18..f62000e 100644
--- a/src/arch/mips/isa/decoder.isa
+++ b/src/arch/mips/isa/decoder.isa
@@ -1532,7 +1532,7 @@
                     if (Rs<2:0> == 0) {
                         Fd_ud = Fs_ud;
                     } else if (Rs<2:0> == 4) {
-                        if (GuestByteOrder == BigEndianByteOrder)
+                        if (GuestByteOrder == ByteOrder::big)
                             Fd_ud = Fs_ud<31:0> << 32 | Ft_ud<63:32>;
                         else
                             Fd_ud = Ft_ud<31:0> << 32 | Fs_ud<63:32>;
diff --git a/src/arch/mips/isa/formats/mem.isa b/src/arch/mips/isa/formats/mem.isa
index 4f6f2ee..491dd0c 100644
--- a/src/arch/mips/isa/formats/mem.isa
+++ b/src/arch/mips/isa/formats/mem.isa
@@ -497,7 +497,7 @@
         uint32_t mem_word = Mem_uw;
         uint32_t unalign_addr = Rs + disp;
         uint32_t byte_offset = unalign_addr & 3;
-        if (GuestByteOrder == BigEndianByteOrder)
+        if (GuestByteOrder == ByteOrder::big)
             byte_offset ^= 3;
     '''
 
@@ -515,7 +515,7 @@
         uint32_t mem_word = 0;
         uint32_t unaligned_addr = Rs + disp;
         uint32_t byte_offset = unaligned_addr & 3;
-        if (GuestByteOrder == BigEndianByteOrder)
+        if (GuestByteOrder == ByteOrder::big)
             byte_offset ^= 3;
         fault = readMemAtomicLE(xc, traceData, EA, mem_word, memAccessFlags);
     '''