[boot] Don't double-load read-only program data

The bootloader's load_program was reproducing all loadable program
header sections into new pages. Now only do that for sections containing
BSS sections (eg, where file size and mem size do not match).

src/boot/paging.cpp

@@ -256,17 +256,14 @@ map_section(
 {
 	using kernel::init::section_flags;
 
-	size_t pages = memory::bytes_to_pages(section.size);
-
 	map_pages(
 		args,
 		section.phys_addr,
 		section.virt_addr,
-		pages,
+		memory::bytes_to_pages(section.size),
 		has_flag(section.type, section_flags::write),
 		has_flag(section.type, section_flags::execute));
 }
 
-
 } // namespace paging
 } // namespace boot