feat(build): check that .text section starts at page boundary

Linker may decide to put new unspecified sections before .text
section. That will cause non-working image, because entry point isn't
at __BLXX_START__. Device just not booted with such image.

This happened for example with .note.gnu.build-id section generated
for LTO build in some cases. Now linker will report this situation as
an error.

```
/usr/lib/gcc-cross/aarch64-linux-gnu/13/../../../../aarch64-linux-gnu/bin/ld: .text is not aligned on a page boundary.
collect2: error: ld returned 1 exit status
```

Signed-off-by: Andrey Skvortsov <andrej.skvortzov@gmail.com>
Change-Id: I5ae46ddd1e6e431e1df1715d1d301f6dd7181cc7
diff --git a/bl1/bl1.ld.S b/bl1/bl1.ld.S
index 49dda85..d25ec63 100644
--- a/bl1/bl1.ld.S
+++ b/bl1/bl1.ld.S
@@ -36,6 +36,9 @@
 
 #if SEPARATE_CODE_AND_RODATA
     .text . : {
+        ASSERT(. == ALIGN(PAGE_SIZE),
+        ".text address is not aligned on a page boundary.");
+
         __TEXT_START__ = .;
 
         *bl1_entrypoint.o(.text*)
@@ -80,6 +83,9 @@
     } >ROM
 #else /* SEPARATE_CODE_AND_RODATA */
     .ro . : {
+        ASSERT(. == ALIGN(PAGE_SIZE),
+        ".ro address is not aligned on a page boundary.");
+
         __RO_START__ = .;
 
         *bl1_entrypoint.o(.text*)