Since SOC_FOO should be deprecated from patch [1], and cleanup for other
SoCs is already in the mailing list [2,3,4], we remove the use of
SOC_CANAAN and use ARCH_CANAAN for SoCs vendored by Canaan instead from now
on. And allows ARCH_CANAAN to be selected for other Canaan SoCs. However,
we should keep the config SOC_CANAAN and use def_bool to redirect the
symbol temporarily to avoid potential conflict.

Since we now have Canaan Kendryte K230 with MMU, ARCH_CANAAN is no longer
referred to as K210. There are some special features for K210, like M-Mode
No MMU and loader.bin in arch/riscv/Makefile. If we keep ARCH_CANAAN for
other Canaan SoCs and remove the K210, the depends on !MMU in Kconfig may
confuse some users who try to boot Kernel with MMU on K210, as Damien
mentioned in the list [5]. Thus, we introduce a new symbol SOC_CANAAN_K210
for any conditional code or driver selection specific to the K210, so users
will not try to build some K210-specific things when MMU is enabled and see
it fails to boot on K210.

[1] https://lore.kernel.org/linux-riscv/20221121221414.109965-1-conor@kernel.org/
[2] https://lore.kernel.org/linux-riscv/20240305-praying-clad-c4fbcaa7ed0a@spud/
[3] https://lore.kernel.org/linux-riscv/20240305-fled-undrilled-41dc0c46bb29@spud/
[4] https://lore.kernel.org/linux-riscv/20240305-stress-earflap-d7ddb8655a4d@spud/
[5] https://lore.kernel.org/linux-riscv/2b0511af-1b5b-4c90-a673-c9113bb58142@kernel.org/Signed-off-by: Yangyu Chen <cyy@cyyself.name>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>