x86/boot: Move boot_*msr helpers to asm/shared/msr.h

x86/boot: Move boot_*msr helpers to asm/shared/msr.h

The boot_{rdmsr,wrmsr}() helpers are *just* the barebones MSR access
functionality, without any tracing or exception handling glue as it is done in
kernel proper.

Move these helpers to asm/shared/msr.h and rename to raw_{rdmsr,wrmsr}() to
indicate what they are.

  [ bp: Correct the reason why those helpers exist. I should've caught that in
    the original patch that added them:
      176db622573f ("x86/boot: Introduce helpers for MSR reads/writes"
    but oh well...
    - fixup include path delimiters to <> ]

Signed-off-by: John Allen <john.allen@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://patch.msgid.link/all/20250924200852.4452-2-john.allen@amd.com