Implement driver architecture with linker-section registration (AI)

- Created driver framework with probe/init lifecycle. Drivers register via
  REGISTER_DRIVER macro which places pointers in a .drivers linker section.
- During boot, init_drivers() iterates the section, probes each driver
  (checking if hardware is present), and initializes those that respond OK.
- Added .drivers section to linker.ld with __drivers_start/__drivers_end
  symbols for iteration.
- Also added .rodata.* pattern to the .rodata section for string literals
  placed in sub-sections by the compiler.
- No drivers are registered yet; the VGA driver will be the first.

Tested: boots cleanly with driver scan completing (0 registered, 0 loaded).

src/linker.ld

@@ -15,6 +15,14 @@ SECTIONS
 	.rodata BLOCK(4K) : ALIGN(4K)
 	{
 		*(.rodata)
+		*(.rodata.*)
+	}
+
+	.drivers BLOCK(4K) : ALIGN(4K)
+	{
+		__drivers_start = .;
+		KEEP(*(.drivers))
+		__drivers_end = .;
 	}
 
 	.data BLOCK(4K) : ALIGN(4K)