spi: Add DMA mode support to spi-qcom-qspi

Merge series from Vijaya Krishna Nivarthi <quic_vnivarth@quicinc.com>:

There are large number of QSPI irqs that fire during boot/init and later
on every suspend/resume.
This could be made faster by doing DMA instead of PIO.
Below is comparison for number of interrupts raised in 2 scenarios...
Boot up and stabilise
Suspend/Resume

Sequence   PIO    DMA
=======================
Boot-up    69088  19284
S/R        5066   3430

Speed test results...
spi-nor read times in sec after 2 min uptime
============================================
PIO - Iterations-1000, min=3.18, max=3.74, avg=3.53
DMA - Iterations-1000, min=1.21, max=2.28, avg=1.79

spi-nor write times in sec after 2 min uptime
=============================================
PIO - Iterations-1000, min=3.20, max=8.24, avg=3.58
DMA - Iterations-1000, min=1.25, max=5.13, avg=1.82

Further testing performed...
a) multiple entries in sgt (simulated by max_dma_len = 1024)
b) fallback to pio (simulated by dma setup failure)

Documentation/devicetree/bindings/spi/qcom,spi-qcom-qspi.yaml

@@ -29,6 +29,9 @@ properties:
   reg:
     maxItems: 1
 
+  iommus:
+    maxItems: 1
+
   interrupts:
     maxItems: 1