x86: Update linker scripts to ensure appended device tree is aligned

With commit 0535e46d55 ("scripts/dtc: Update to upstream version
v1.7.2-35-g52f07dcca47c") it is now a fatal error to U-Boot if our
device tree is not 8-byte aligned. In commit 85f586035d ("ARM: OMAP2+:
Pad SPL binary to 8-byte alignment before DTB") Beleswar Padhi explains
that we must have ALIGN(x) statements inside of a section to ensure that
padding is included and not simply that the linker address counter is
incremented. To that end, this patch:
- Rewrite the '.rel.dyn' (u-boot.lds) to follow modern practices, and
  include the 8-byte alignment at the end of the section.
- Expands the '.dynamic' section (u-boot-64.lds) to be more readable
  when adding a second statement to the section.
- Aligns the final section before _end (for U-Boot) or _image_binary_end
  or __bss_end (for xPL phases) by 8-bytes by adding '. = ALIGN(8);' to
  the final section before the symbol or changing an existing ALIGN(4)
  statement.
- Ensure that we do have alignment by adding an ASSERT so that when not
  aligned we fail to link (and explain why).

Signed-off-by: Tom Rini <trini@konsulko.com>

arch/x86/cpu/u-boot-64.lds

@@ -86,9 +86,11 @@ SECTIONS
 	__rel_dyn_end = .;
 	. = ALIGN(4);
 
-	.dynamic : { *(.dynamic) }
+	.dynamic : {
+		*(.dynamic)
+		. = ALIGN(8);
+	}
 
-	. = ALIGN(4);
 	_end = .;
 
 	.bss __rel_dyn_start (OVERLAY) : {

arch/x86/cpu/u-boot-spl.lds

@@ -68,7 +68,7 @@ SECTIONS
 		__bss_start = .;
 		*(.bss*)
 		*(COM*)
-		. = ALIGN(4);
+		. = ALIGN(8);
 		__bss_end = .;
 	}
 	__bss_size = __bss_end - __bss_start;
@@ -97,3 +97,11 @@ SECTIONS
 #endif
 
 }
+
+ASSERT(_image_binary_end % 8 == 0, \
+       "_image_binary_end must be 8-byte aligned for device tree");
+
+#if !CONFIG_IS_ENABLED(SEPARATE_BSS)
+ASSERT(__bss_end % 8 == 0, \
+       "__bss_end must be 8-byte aligned for device tree");
+#endif

arch/x86/cpu/u-boot.lds

@@ -79,13 +79,12 @@ SECTIONS
 	. = ALIGN(4);
 	.dynsym : { *(.dynsym*) }
 
-	. = ALIGN(4);
-	__rel_dyn_start = .;
-	.rel.dyn : {
+	.rel.dyn ALIGN(4) : {
+		__rel_dyn_start = .;
 		*(.rel*)
+		__rel_dyn_end = .;
+		. = ALIGN(8);
 	}
-	__rel_dyn_end = .;
-	. = ALIGN(4);
 	_end = .;
 
 	.bss __rel_dyn_start (OVERLAY) : {
@@ -120,3 +119,5 @@ SECTIONS
 #endif
 
 }
+
+ASSERT(_end % 8 == 0, "_end must be 8-byte aligned for device tree");