x86/boot/e820: Standardize e820 table index variable types under 'u32'

x86/boot/e820: Standardize e820 table index variable types under 'u32'

So we have 'idx' types of 'int' and 'unsigned int', and sometimes
we assign 'u32' fields such as e820_table::nr_entries to these 'int'
values.

While there's no real risk of overflow with these tables, make it
all cleaner by standardizing on a single type: u32.

This also happens to shrink the code a bit:

   text      data      bss        dec        hex    filename
   7745     44072        0      51817       ca69    e820.o.before
   7613     44072        0      51685       c9e5    e820.o.after

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: H . Peter Anvin <hpa@zytor.com>
Cc: Andy Shevchenko <andy@kernel.org>
Cc: Arnd Bergmann <arnd@kernel.org>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Paul Menzel <pmenzel@molgen.mpg.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20250515120549.2820541-19-mingo@kernel.org