Improve polling mode of s3c64xx driver

Merge series from Jaewon Kim <jaewon02.kim@samsung.com>:

Previously, polling mode was supported as quirk for SOC without DMA.
In order to use it more flexibly, it is supported when there is
no dmas property in devicetree, and the issue of using excessive CPU
usage in polling mode is solved by adding sleep during transfer time and
supporting interrupt mode.

Changes in V3.
- Fix patch commit message.
- Change of_find_property() to of_property_present() with code cleanup
- Remove cpu_relax() related patch.
- Changes use_irq variable type to bool

Changes in V2.
- Switched to polling mode if there is no dmas property in devicetree.
- Add cpu_releax() in polling loop
- Add lower limit in IRQ mode

Jaewon Kim (3):
  spi: s3c64xx: change polling mode to optional
  spi: s3c64xx: add sleep during transfer
  spi: s3c64xx: support interrupt based pio mode

 drivers/spi/spi-s3c64xx.c                 | 81 +++++++++++++++++++----
 include/linux/platform_data/spi-s3c64xx.h |  1 +
 2 files changed, 70 insertions(+), 12 deletions(-)

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2.17.1