XIP adaptation for xtensa platform (#1636)

Add macro WASM_ENABLE_WORD_ALING_READ to enable reading
1/2/4 and n bytes data from vram buffer, which requires 4-byte addr
alignment reading.

Eliminate XIP AOT relocations related to the below ones:
   i32_div_u, f32_min, f32_max, f32_ceil, f32_floor, f32_trunc, f32_rint

core/config.h

@@ -70,6 +70,10 @@
 #define WASM_ENABLE_AOT 0
 #endif
 
+#ifndef WASM_ENABLE_WORD_ALIGN_READ
+#define WASM_ENABLE_WORD_ALIGN_READ 0
+#endif
+
 #define AOT_MAGIC_NUMBER 0x746f6100
 #define AOT_CURRENT_VERSION 3