i386 bootioremap / kexec fix

With CONFIG_PHYSICAL_START set to a non default values the i386
boot_ioremap code calculated its pte index wrong and users of boot_ioremap
have their areas incorrectly mapped (for me SRAT table not mapped during
early boot).  This patch removes the addr < BOOT_PTE_PTRS constraint.

Signed-off-by: Keith Mannthey <kmannth@us.ibm.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>