intelspi: add PCI attachment (Lynx/Wildcat/Sunrise Point)

Also adds fixups and cleanups:

• apply the child's mode/speed
• implement suspend/resume support
• use RF_SHAREABLE interrupts
• use bus_delayed_attach_children since the transfer can use interrupts
• add support for newly added spibus features (cs_delay and flags)

Operation tested on Broadwell (Wildcat Point) MacBookPro12,1.
Attachment also tested on Kaby Lake (Sunrise Point) Pixelbook.

Reviewed by: wulf
MFC after: 1 month
Differential revision: https://reviews.freebsd.org/D29249