[U-Boot] [Patch v2] spi: mxc-spi: fixes for ECSPI

This series improver the original one:

- split first patch into two patches - add only the register fields that are needed for clk control - better comments

[PATCH 1/3] spi: spi-mxc: add defines for clk inactive state for [PATCH 2/3] spi: spi-mxc: implement clk control for ECSPI to fix [PATCH 3/3] spi: mxc_spi: i.MX6 DL/S have only 4 eCSPI controller