mips: cm: Convert __mips_cm_l2sync_phys_base() to weak function

mips: cm: Convert __mips_cm_l2sync_phys_base() to weak function

[ Upstream commit 8bc8db2ab2832daabdd06feeabdd511dc9575bb6 ]

The __mips_cm_l2sync_phys_base() and mips_cm_l2sync_phys_base() couple was
introduced in commit 9f98f3dd0c51 ("MIPS: Add generic CM probe & access
code") where the former method was a weak implementation of the later
function. Such design pattern permitted to re-define the original method
and to use the weak implementation in the new function. A similar approach
was introduced in the framework of another arch-specific programmable
interface: mips_cm_phys_base() and __mips_cm_phys_base(). The only
difference is that the underscored method of the later couple was declared
in the "asm/mips-cm.h" header file, but it wasn't done for the CM L2-sync
methods in the subject. Due to the missing global function declaration
the "missing prototype" warning was spotted in the framework of the commit
9a2036724cd6 ("mips: mark local function static if possible") and fixed
just be re-qualifying the weak method as static. Doing that broke what was
originally implied by having the weak implementation globally defined.

Let's fix the broken CM2 L2-sync arch-interface by dropping the static
qualifier and, seeing the implemented pattern hasn't been used for over 10
years but will be required soon (see the link for the discussion around
it), converting it to a single weakly defined method:
mips_cm_l2sync_phys_base().

Fixes: 9a2036724cd6 ("mips: mark local function static if possible")
Link: https://lore.kernel.org/linux-mips/20240215171740.14550-3-fancer.lancer@gmail.com
Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>