x86/boot/e820: Print E820_TYPE_RAM entries as ... RAM entries

x86/boot/e820: Print E820_TYPE_RAM entries as ... RAM entries

So it is a bit weird that the actual RAM entries of the E820 table
are not actually called RAM, but 'usable':

	BIOS-e820: [mem 0x0000000000100000-0x000000007ffdbfff]    1.9 GB usable

'usable' is pretty passive-aggressive in that context and ambiguous,
most E820 entries denote 'usable' address ranges - reserved ranges
may be used by devices, or the platform.

Clarify and disambiguate this by making the boot log entry
explicitly say 'System RAM', like in /proc/iomem:

	BIOS-e820: [mem 0x0000000000100000-0x000000007ffdbfff]    1.9 GB System RAM

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Shevchenko <andy@kernel.org>
Cc: Arnd Bergmann <arnd@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Juergen Gross <jgross@suse.com>
Cc: "H . Peter Anvin" <hpa@zytor.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>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Link: https://patch.msgid.link/20250515120549.2820541-9-mingo@kernel.org