mutex: move mutex calls to .sched.text

We move mutex calls to its own sub-section, underneath .text.
We'll next try to use the standard section work we've been doing
to see how this will fit as sub-sections within the framework.

readelf -S kernel/locking/mutex.o | grep sched
  [ 6] .sched.text       PROGBITS         0000000000000000  000000b0
  [ 7] .rela.sched.text  RELA             0000000000000000  00001368

When we run ./main:

Initializing x86 bare metal world
x86-init: Number of init entries: 7
Initializing kasan ...
Early init for Kasan...
Completed initializing kasan !
Initializing memory ...
Completed initializing memory !
Initializing kprobes ...
== OK: test_kprobe_0001 within range!
== OK: test_kprobe_0002 not in range as expected!
Completed initializing kprobes !
Initializing pci ...
PCI fixup size: 1
Demo: Using LINKTABLE_FOR_EACH
foo_fixup
Demo: Using LINKTABLE_RUN_ALL
foo_fixup
Completed initializing pci !
Initializing beta ...
Completed initializing beta !
Initializing alpha ...
Completed initializing alpha !
Booting bare metal
Calling start_kernel()...
ACME: Initializing ...
ACME: Finished init ... !
ACME: Running scheduled work

Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>