UPSTREAM: arm64: mm: remove unused cpu_set_idmap_tcr_t0sz function

With commit b08d4640a3dc ("arm64: remove dead code"),
cpu_set_idmap_tcr_t0sz is no longer called and can therefore be removed
from the kernel.

This patch removes the function and effectively inlines the helper
function __cpu_set_tcr_t0sz into cpu_set_default_tcr_t0sz.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Bug: 31432001
Change-Id: Iaa84a9f88af57c26ba2f80746888965ac636a2b3
(cherry picked from commit c51e97d89e526368eb697f87cd4d391b9e19f369)
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>