Summary:
I2C trackpad doesn't work on Lenovo Yoga 700-11ISK, due to an interrupt conflict between pata_legacy and sunrisepoint-pinctrl.

Kernel log (excerpts):
    [  +0.000209] genirq: Flags mismatch irq 14. 00000080 (INT344B:00) vs. 00000000 (platform[pata_legacy.0])

    [  +0.000079] sunrisepoint-pinctrl INT344B:00: failed to request interrupt
    [  +0.020469] sunrisepoint-pinctrl: probe of INT344B:00 failed with error -16

    [  +0.226303] i2c_hid i2c-ITE8350:00: Failed to get GPIO interrupt
    [  +0.009366] i2c_hid: probe of i2c-ITE8350:00 failed with error -2
    [  +0.019873] i2c_hid i2c-SYNA2B23:00: Failed to get GPIO interrupt
    [  +0.012687] i2c_hid: probe of i2c-SYNA2B23:00 failed with error -2

Analysis:
- pata_legacy acquires IRQ 14 without IRQF_SHARED.
- the pin controller (sunrise point) is therefore unable to initialise the GPIO chip
- i2c_hid then fails on calling gpiod_get()
- trackpad is connected via I2C, and therefore unusable

Workaround:
pata_legacy is an IDE driver, and therefore not needed on a modern laptop. Since it's included in the initrd, blacklisting via modprobe.d is insufficient - it needs to be either blacklisted via a kernel parameter or removed from the initrd completely (how to best do this is distro-specific).

Possible fix:
pata_legacy should release the interrupt after it has established there are no IDE devices present.

Additional notes:
This affects kernel 4.4 and later. 4.3 is unaffected.
Tested under Sabayon amd64.

Since Sunrise Point is the chipset used with Intel Skylake CPUs, other Skylake devices may be affected.