Bug: Example MPU 4.1 broken due to missing linker script support

[arctic-alpaca]

Example 4.1 tries to read the flag from

veecle-pxros/examples/example-mpu/src/ex4_1.rs

Line 7 in cd807ed

const DATA_ADDRESS: usize = 0xB002FC00;

which should refer to

veecle-pxros/examples/example-mpu/src/backend.rs

Lines 11 to 13 in cd807ed

	#[cfg_attr(target_os = "macos", link_section = ".uninit,mpu_protected")]
	#[cfg_attr(not(target_os = "macos"), link_section = ".mpu_protected")]
	static FLAG_4_1: [u8; 16] = *b"OsU7rwolFq3ItiJ5"; // Keep this at 16 characters always, this is hardcoded

. Due to there being no linker script entry, the flag is not included at the expected location and example 4.1 fails.

We should either revamp the example or include optional linker script support again.