hw/misc: Add NPCM7xx Clock Controller device model

hw/misc: Add NPCM7xx Clock Controller device model

Enough functionality to boot the Linux kernel has been implemented. This
includes:

  - Correct power-on reset values so the various clock rates can be
    accurately calculated.
  - Clock enables stick around when written.

In addition, a best effort attempt to implement SECCNT and CNTR25M was
made even though I don't think the kernel needs them.

Reviewed-by: Tyrone Ting <kfting@nuvoton.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Alexander Bulekov <alxndr@bu.edu>
Signed-off-by: Havard Skinnemoen <hskinnemoen@google.com>
Message-id: 20200911052101.2602693-3-hskinnemoen@google.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>