OPAL implements firmware calls that abstract communicating with the BMC over
IPMI. Use these calls to add support for impi(4) on PowerNV systems.

ok dlg@

Only use OPAL_CONSOLE_FLUSH if the firmware implements it. Should help
on POWER8 machines with older versions of OPAL.

Add OPAL_PCI_MAP_PE_DMA_WINDOW.

Add OPAL_SET_XIVE and OPAL_GET_XIVE.

Add OPAL_START_CPU.

Add OPAL_REINIT_CPUS.

Add opalsens(4), a driver for sensors provided by the OPAL firmware.

Flush OPAL console when writing kernel messages. Removes annoying delay
before kernel messages show up on the serial console.

Handle OPAL interrupts.

Get context switching between kernel threads going.

Since the stacks for kernel threads are not mapped 1:1 this involves
translating virtual addresses into physical addresses when making
OPAL calls.

Add support for the XIVE interrupt controller found on POWER9 CPUs.

Another OPAL API that we need.

Add MSI support calls.

Add RTC read and write calls.

More OPAL interfaces.

Add more return codes.

Add functions to read/write from/to PCI config space.

Enter ddb at a trap instruction or with db_enter().

Tell make that trap_subr.S needs assym.h.
Fill in opal_cngetc() so I can type at the "ddb>" prompt.
Add enough code to trap_subr.S to "c" continue

Enter ddb at a trap instruction or with db_enter().

Tell make that trap_subr.S needs assym.h.
Fill in opal_cngetc() so I can type at the "ddb>" prompt.
Add enough code to trap_subr.S to "c" continue from ddb.
Give registers to ddb.
Try to load symbols from initrd.

ok kettenis@

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Clean up the code that implements the OPAL API.