x86/acpi: Replace manual page table initialization with kernel_ident_mapping_init()

The init_transition_pgtable() functions maps the page with
asm_acpi_mp_play_dead() into an identity mapping.

Replace open-coded manual page table initialization with
kernel_ident_mapping_init() to avoid code duplication.

Use x86_mapping_info::offset to get the page mapped at the
correct location.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20241016111458.846228-3-kirill.shutemov@linux.intel.com