x86/boot/e820: Harmonize the 'struct e820_table' fields

So the e820_table->map and e820_table->nr_map names are a bit
confusing, because it's not clear what a 'map' really means
(it could be a bitmap, or some other data structure), nor is
it clear what nr_map means (is it a current index, or some
other count).

Rename the fields from:

 e820_table->map        =>     e820_table->entries
 e820_table->nr_map     =>     e820_table->nr_entries

which makes it abundantly clear that these are entries
of the table, and that the size of the table is ->nr_entries.

Propagate the changes to all affected files. Where necessary,
adjust local variable names to better reflect the new field names.

No change in functionality.

Cc: Alex Thorlton <athorlton@sgi.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Huang, Ying <ying.huang@intel.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Jackson <pj@sgi.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>