Adding platform detection opcodes + fix assembler bug.

Adding flags to allow runtime detection of different esp32 models,
riscv vs xtensa, and psram.

Use this to conditionally compile hook for relevant assemblers.

esp32/platform.h

@@ -0,0 +1,55 @@
+// Copyright 2023 Bradley D. Nelson
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#if defined(CONFIG_IDF_TARGET_ESP32)
+# define UEFORTH_PLATFORM_IS_ESP32 (-1)
+#else
+# define UEFORTH_PLATFORM_IS_ESP32 0
+#endif
+
+#if defined(CONFIG_IDF_TARGET_ESP32S2)
+# define UEFORTH_PLATFORM_IS_ESP32S2 (-1)
+#else
+# define UEFORTH_PLATFORM_IS_ESP32S2 0
+#endif
+
+#if defined(CONFIG_IDF_TARGET_ESP32S3)
+# define UEFORTH_PLATFORM_IS_ESP32S3 (-1)
+#else
+# define UEFORTH_PLATFORM_IS_ESP32S3 0
+#endif
+
+#if defined(CONFIG_IDF_TARGET_ESP32C3)
+# define UEFORTH_PLATFORM_IS_ESP32C3 (-1)
+#else
+# define UEFORTH_PLATFORM_IS_ESP32C3 0
+#endif
+
+#if defined(BOARD_HAS_PSRAM)
+# define UEFORTH_PLATFORM_HAS_PSRAM (-1)
+#else
+# define UEFORTH_PLATFORM_HAS_PSRAM 0
+#endif
+
+#if defined(__XTENSA__)
+# define UEFORTH_PLATFORM_IS_XTENSA (-1)
+#else
+# define UEFORTH_PLATFORM_IS_XTENSA 0
+#endif
+
+#if defined(__riscv)
+# define UEFORTH_PLATFORM_IS_RISCV (-1)
+#else
+# define UEFORTH_PLATFORM_IS_RISCV 0
+#endif