[XLA:GPU] Convert Cholesky custom call in XLA HLO to LHLO GPU Dialect.

- Restructured LHLO GPU Cholesky to better match XLA HLO by eliminating the
  untyped buffer and changing is_upper attribute to is_lower.
- Change LhloDialectEmitter to emit LHLO GPU Cholesky operation.

PiperOrigin-RevId: 343873516

include/mlir-hlo/Dialect/mhlo/IR/lhlo_gpu_ops.td

@@ -202,9 +202,9 @@ def LHLOGPU_CholeskyOp : LHLOGPU_Op<"cholesky"> {
   let arguments = (ins
     Arg<LHLO_Buffer, "", [MemRead]>:$input,
     Arg<LHLO_Buffer, "", [MemWrite]>:$output,
-    Arg<UntypedBuffer, "", [MemWrite]>:$scratch,
+    Arg<LHLO_Buffer, "", [MemWrite]>:$scratch,
     Arg<I32Buffer, "", [MemWrite]>:$info,
-    BoolAttr:$is_upper);
+    BoolAttr:$is_lower);
 }
 
 #endif // LHLO_GPU_OPS

tests/lhlo_gpu_ops.mlir

@@ -93,7 +93,7 @@ func @gemm_bias(%lhs: memref<5x4xf32>, %rhs: memref<4x5xf32>,
 func @cholesky(%arg : memref<10x10xf32>, %out: memref<10x10xf32>) {
   %scratch = alloc() : memref<32xi8>
   %info = alloc() : memref<32xi32>
-  "lmhlo_gpu.cholesky"(%arg, %out, %scratch, %info) { is_upper = true }
+  "lmhlo_gpu.cholesky"(%arg, %out, %scratch, %info) { is_lower = true }
       : (memref<10x10xf32>, memref<10x10xf32>, memref<32xi8>, memref<32xi32>) -> ()
   return
 }