riscv: Update alignment for some sections in linker scripts

Some sections in the linker scripts are aligned to 4 bytes, which
may cause misaligned exception on some platforms, e.g.: clearing
the bss section on 64-bit hardware if __bss_start does not start
from a naturally 8 bytes aligned address.

Signed-off-by: Bin Meng <bmeng@tinylab.org>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>

arch/riscv/cpu/u-boot-spl.lds

@@ -44,7 +44,7 @@ SECTIONS
 		__binman_sym_end = .;
 	} > .spl_mem
 
-	. = ALIGN(4);
+	. = ALIGN(8);
 
 	_end = .;
 	_image_binary_end = .;

arch/riscv/cpu/u-boot.lds

@@ -57,7 +57,7 @@ SECTIONS
 		__efi_runtime_rel_stop = .;
 	}
 
-	. = ALIGN(4);
+	. = ALIGN(8);
 
 	/DISCARD/ : { *(.rela.plt*) }
 	.rela.dyn : {
@@ -66,7 +66,7 @@ SECTIONS
 		__rel_dyn_end = .;
 	}
 
-	. = ALIGN(4);
+	. = ALIGN(8);
 
 	.dynsym : {
 		__dyn_sym_start = .;
@@ -74,7 +74,7 @@ SECTIONS
 		__dyn_sym_end = .;
 	}
 
-	. = ALIGN(4);
+	. = ALIGN(8);
 
 	_end = .;