spi: STIG Mode Fixes for spi-cadence-qspi driver

spi: STIG Mode Fixes for spi-cadence-qspi driver

Merge series from Dhruva Gole <d-gole@ti.com>:

* Reset the CMD_CTRL Register, without which read/writes in STIG mode
were failing in some cases. The issue came to light while using STIG
Mode for small reads.
* Also add a flag that can allow us to do direct reads but distinguish
direct writes, thus enabling us to disable writes in DAC mode in some
cases that require it. (Like to write to some connected Flash registers)
* Fix register reads in STIG mode and also use STIG mode while reading flash
registers.
Currently if you try to read a register while in STIG mode there is no
support for ADDR and thus naturally a register never gets read from the
flash.

This patch series has been tested on a TI AM625-SK-EVM with both a quad
spi nor flash (s25hs) and OSPI NOR Flash (s28hs).

Output of ltp-ddt test, "DD_RW_ERASESIZE_UBIFS" run with s25hs512t flash:
...
[    2.334068] spi-nor spi0.0: s25hs512t (65536 Kbytes)
[    2.339185] 7 fixed-partitions partitions found on MTD device
fc40000.spi.0
[    2.346158] Creating 7 MTD partitions on "fc40000.spi.0":
[    2.351555] 0x000000000000-0x000000080000 : "ospi.tiboot3"
[    2.358344] 0x000000080000-0x000000280000 : "ospi.tispl"
[    2.364788] 0x000000280000-0x000000680000 : "ospi.u-boot"
[    2.371311] 0x000000680000-0x0000006c0000 : "ospi.env"
[    2.377519] 0x0000006c0000-0x000000700000 : "ospi.env.backup"
[    2.384419] 0x000000800000-0x000003fc0000 : "ospi.rootfs"
[    2.390890] 0x000003fc0000-0x000004000000 : "ospi.phypattern"
..snip..
Test Start Time: Wed Jan 11 21:14:31 2023
-----------------------------------------
Testcase                                           Result     Exit Value
--------                                           ------     ----------
OSPI_S_FUNC_DD_RW_ERASESIZE_UBIFS                  PASS       0

-----------------------------------------------
Total Tests: 1
Total Skipped Tests: 0
Total Failures: 0
Kernel Version: 6.2.0-rc1-00040-g700d796a94e0-dirty
Machine Architecture: aarch64
Hostname: am62xx-evm