Add the 'bletchley-bmc' machine type based on the kernel DTS[1] and
hardware schematics available to me.  The i2c model is as complete as
the current QEMU models support, but in some cases I substituted devices
that are close enough for present functionality.  Strap registers are
kept the same as the AST2600-EVB until I'm able to confirm correct
values with physical hardware.

This has been tested with an openbmc image built from [2] plus a kernel
patch[3] for the SPI flash module.

1. https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/arch/arm/boot/dts/aspeed-bmc-facebook-bletchley.dts?id=a8c729e966c4e9d033242d948b0e53c2a62d32e2
2. https://github.com/openbmc/openbmc/commit/b9432b980d7f63f7512ffbcc7124386ba896dfc6
3. https://github.com/openbmc/linux/commit/25b566b9a9d7f5d4f10c1b7304007bdb286eefd7



Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
[ clg : increased number of FMC devices to 2 to match Linux dts ]
Message-Id: <20220305000656.1944589-2-patrick@stwcx.xyz>
Signed-off-by: Cédric Le Goater <clg@kaod.org>