Kernel Early Print

Before the first early prink, __create_page_tables in arch/arm/kernel/head.S will create mapping entry of IO space for UART.

 /*
  * Map in IO space for serial debugging.
  * This allows debug messages to be output
  * via a serial console before paging_init.
  */
 addruart r7, r3, r0

 mov r3, r3, lsr #SECTION_SHIFT
 mov r3, r3, lsl #PMD_ORDER

 add r0, r4, r3
 mov r3, r7, lsr #SECTION_SHIFT
 ldr r7, [r10, #PROCINFO_IO_MMUFLAGS] @ io_mmuflags
 orr r3, r7, r3, lsl #SECTION_SHIFT