[boot][kernel] Split programs into sections

To enable setting sections as NX or read-only, the boot program loader
now loads programs as lists of sections, and the kernel args are updated
accordingly. The kernel's loader now just takes a program pointer to
iterate the sections. Also enable NX in IA32_EFER in the bootloader.

src/boot/paging.h

@@ -38,15 +38,14 @@ void allocate_tables(
 /// tables in the current PML4.
 void add_current_mappings(page_table *new_pml4);
 
-/// Map a physical address to a virtual address in the given page tables.
-/// \arg args  The kernel args header, used for the page table cache and pml4
-/// \arg phys  The phyiscal address to map in
-/// \arg virt  The virtual address to map in
-/// \arg size  The size in bytes of the mapping 
-void map_pages(
+/// Map a program section in physical memory to its virtual address in the
+/// given page tables.
+/// \arg args    The kernel args header, used for the page table cache and pml4
+/// \arg section The program section to load
+void map_section(
 	kernel::args::header *args,
-	uintptr_t phys, uintptr_t virt,
-	size_t bytes);
+	const kernel::args::program_section &section);
+
 
 } // namespace paging
 } // namespace boot