x86: Factor out e820_add_kernel_range()

Separate out the reservation of the kernel static memory areas into a
separate function.

Also add support for case when memmap=xxM$yyM is used without exactmap.
Need to remove reserved range at first before we add E820_RAM
range, otherwise added E820_RAM range will be ignored.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Link: http://lkml.kernel.org/r/1359058816-7615-5-git-send-email-yinghai@kernel.org
Cc: Jacob Shin <jacob.shin@amd.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>