This patch adds driver for Cadence's XSPI controller.
It supports 3 work modes.
1. ACMD (auto command) work mode
    ACMD name is because it uses auto command engine in the controller.
    It further has 2 modes PIO and CDMA (command DMA).
    The CDMA work mode is dedicated for high-performance application
    where very low software overhead is required. In this mode the
    Command Engine is programmed by the series of linked descriptors
    stored in system memory. These descriptors provide commands to execute
    and store status information for finished commands.
    The PIO mode work mode is dedicated for single operation where
    constructing a linked list of descriptors would require too
    much effort.
2. STIG (Software Triggered Instruction Generator) work mode
    In STIG mode, controller sends low-level instructions to memory.
    Each instruction is 128-bit width. There is special instruction
    DataSequence which carries information about data phase.
    Driver uses Slave DMA interface to transfer data as only this
    interface can be used in STIG work mode.
3. Direct work mode
    This work mode allows sending data without invoking any command through
    the slave interface.
Currently only STIG work mode is enabled, remaining work modes will
be added later.
Signed-off-by: Konrad Kociolek <konrad@cadence.com>
Signed-off-by: Jayshri Pawar <jpawar@cadence.com>
Signed-off-by: Parshuram Thombare <pthombar@cadence.com>
Acked-by: Pratyush Yadav <p.yadav@ti.com>
Link: https://lore.kernel.org/r/1632038734-23999-1-git-send-email-pthombar@cadence.comSigned-off-by: Mark Brown <broonie@kernel.org>