disable MMU and data cache

#ifndef CONFIG_SKIP_LOWLEVEL_INIT_ONLY
	/*
	 * Jump to board specific initialization... The Mask ROM will have already initialized
	 * basic memory.  Go here to bump up clock rate and handle wake up conditions.
	 */
	mov	ip, lr		/* persevere link reg across call */
	bl	lowlevel_init	/* go setup pll,mux,memory */
	mov	lr, ip		/* restore link */
#endif
	mov	pc, lr		/* back to my caller */

Register lr save the return address of the function call, before calling lowlevel_init, restore it to lr after that.

to be continued

It is found that the using the default make cscope there are still a lot of symbols with same name, and it is difficult to following. I have improved the method to create the cscope database in cscope_u-boot_improved and a new post read_u-boot_aarch64_source_code_part1 is added by using the new method.