Bump Skiboot to v6.6-283-gb74318a54

Changes since skiboot-v6.6-268-gc80eab0d3:

Oliver O'Halloran (13):
      external/trace: Fall back to read()
      external/trace: Print timestamps in prlog()'s format
      trace: Add nvram hack to use the old trace export behaviour
      i2c,trace: Add I2C operation trace events
      hw/p8-i2c: Add p8_i2c_find_bus_by_port()
      hw/p8-i2c: Print interrupt status per master
      hw/p8-i2c: Set poll interval from the current port
      hw/p8-i2c: Move port init into a separate function
      hdat/i2c: Rework i2c device creation
      hw/p8-i2c: Add buses at runtime
      hw/p8-i2c: Update OCCFLG register address on P10
      hw/p8-i2c: Fix I2C interrupt on P10
      raininer: power on PCIe slots at boot

Ryan P Grimm (1):
      Merge pull request #61 from oliveroh/rainier-pcie-slot-power

Vaidyanathan Srinivasan (1):
      hw/nx: DARN init for P10 fused core

----------------------------------------------------------------
 core/i2c.c                  |  32 ++++++++++
 core/init.c                 |   3 +
 core/trace.c                |  17 +++---
 external/trace/dump_trace.c |  60 +++++++++++++++++--
 hdata/i2c.c                 | 171 +++++++++++++++++++++++++++++++++-------------------
 hw/nx.c                     |   7 +++
 hw/p8-i2c.c                 | 274 ++++++++++++++++++++++++++++++++++++++++++++++++++++++------------------------------
 include/i2c.h               |  18 +++---
 include/trace.h             |   1 +
 include/trace_types.h       |  12 ++++
 platforms/astbmc/rainier.c  |  87 ++++++++++++++++++++++++++-
 11 files changed, 503 insertions(+), 179 deletions(-)

Signed-off-by: Klaus Heinrich Kiwi <klaus@linux.vnet.ibm.com>
diff --git a/openpower/package/skiboot/Config.in b/openpower/package/skiboot/Config.in
index fe12a25..07e2c20 100644
--- a/openpower/package/skiboot/Config.in
+++ b/openpower/package/skiboot/Config.in
@@ -31,7 +31,7 @@
 
 config BR2_SKIBOOT_VERSION
 	string
-	default "v6.6-268-gc80eab0d3" if BR2_SKIBOOT_LATEST_VERSION
+	default "v6.6-283-gb74318a54" if BR2_SKIBOOT_LATEST_VERSION
 	default BR2_SKIBOOT_CUSTOM_VERSION_VALUE \
 		if BR2_SKIBOOT_CUSTOM_VERSION