x86/e820: Drop obsolete E820_TYPE_RESERVED_KERN and related code

x86/e820: Drop obsolete E820_TYPE_RESERVED_KERN and related code

E820_TYPE_RESERVED_KERN is a relict from the ancient history that was used
to early reserve setup_data, see:

  28bb22379513 ("x86: move reserve_setup_data to setup.c")

Nowadays setup_data is anyway reserved in memblock and there is no point in
carrying E820_TYPE_RESERVED_KERN that behaves exactly like E820_TYPE_RAM
but only complicates the code.

A bonus for removing E820_TYPE_RESERVED_KERN is a small but measurable
speedup of 20 microseconds in init_mem_mappings() on a VM with 32GB or RAM.

Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20250214090651.3331663-5-rppt@kernel.org