Fix boot failure when compiling with Clang/LLD (#69)

- link.lds: Add .rodata section between .text and .data
- start.S: Add .global _start, .type directive, rename entry to _start

Signed-off-by: ann-yanan <yanan.hya@alibaba-inc.com>

Author: ann-yanan

link.lds

@@ -7,6 +7,10 @@ SECTIONS
 		*(.text)
 		PROVIDE(_text_end = .);
 	}
+	.rodata : {
+		*(.rodata)
+		*(.rodata.*)
+	}
 	. = ALIGN(8);
 	.data : {
 		PROVIDE(_data_start = .);

start.S

@@ -1,11 +1,14 @@
 #include "riscv_asm.h"
 #include "riscv_encoding.h"
 
+.global _start
+.type _start, @function
+
 .global _load_start
 
 #define BOOT_STATUS_RELOCATE_DONE	1
 
-entry:
+_start:
 	/*
 	 * Clear L1 cache & BTB & BHT ...
 	 */
@@ -31,7 +34,7 @@ entry:
 	 */
 	lla	t0, _load_start
 	REG_L  t2, 0(t0)
-	lla	t1, entry
+	lla	t1, _start
 	REG_S	t1, 0(t0)
 
 	/*