x86: replace boot_ioremap() with enhanced bt_ioremap() - remove boot_ioremap()

This patch replaces boot_ioremap invokation with bt_ioremap and
removes the boot_ioremap implementation.

Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>