irqchip/sifive-plic: Probe plic driver early for Allwinner D1 platform

The latest Linux RISC-V no longer boots on the Allwinner D1 platform
because the sun4i_timer driver fails to get an interrupt from PLIC due to
the recent conversion of the PLIC to a platform driver. Converting the
sun4i timer to a platform driver does not work either because the D1 does
not have a SBI timer available so early boot hangs. See the 'Closes:'
link for deeper analysis.

The real fix requires enabling the SBI time extension in the platform
firmware (OpenSBI) and convert sun4i_timer into platform driver.
Unfortunately, the real fix involves changing multiple places and can't be
achieved in a short duration and aside of that requires users to update
firmware.

As a work-around, retrofit PLIC probing such that the PLIC is probed early
only for the Allwinner D1 platform and probed as a regular platform driver
for rest of the RISC-V platforms. In the process, partially revert some of
the previous changes because the PLIC device pointer is not available in
all probing paths.

Fixes: e306a894bd51 ("irqchip/sifive-plic: Chain to parent IRQ after handlers are ready")
Fixes: 8ec99b033147 ("irqchip/sifive-plic: Convert PLIC driver into a platform driver")
Suggested-by: Thomas Gleixner <[email protected]>
Signed-off-by: Anup Patel <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Tested-by: Samuel Holland <[email protected]>
Tested-by: Emil Renner Berthing <[email protected]>
Tested-by: Charlie Jenkins <[email protected]>
Reviewed-by: Samuel Holland <[email protected]>
Reviewed-by: Charlie Jenkins <[email protected]>
Cc: [email protected]
Link: https://lore.kernel.org/all/[email protected]
Closes: https://lore.kernel.org/lkml/[email protected]/

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