of/platform: Probe "isa" busses by default

Since commit 44a7185c ("of/platform: Add common method to populate
default bus") platforms calling of_platform_bus_probe from an initcall
is either a rather unsafe race with of_platform_default_populate_init or
a no-op. The MIPS Malta board needs to probe devices under an ISA bus,
which we do support in the of_busses array but until now haven't
included in of_default_bus_match_table.

Add an "isa" entry to of_default_bus_match_table such that we can just
accept use of of_platform_default_populate_init & remove the
Malta-specific match table in a later patch.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Acked-by: Rob Herring <robh@kernel.org>
Cc: Frank Rowand <frowand.list@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/14275/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>