ARM: Fix incorrect panic message.

As noted during BeGeistert and today again by kallisti5, there's a
Pentium reference in the ARM bootloader code.

Correct the message to something more appropriate....

Thanks to Rene for the suggestion ;)

src/system/boot/arch/arm/arch_cpu.cpp

@@ -70,7 +70,7 @@ boot_arch_cpu_init(void)
 	status_t err = check_cpu_features();
 
 	if (err != B_OK) {
-		panic("You need a Pentium or higher in order to boot!\n");
+		panic("Retire your old Acorn and get something modern to boot!\n");
 		return err;
 	}