mfd: Remove htc-i2cpld driver

The HTC Herald machine was removed, so this driver is no
longer used anywhere.

Cc: Cory Maccarrone <darkstar6262@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20221019150410.3851944-17-arnd@kernel.org