POWER9: Bump skiboot to 950577e5dddeb99c1ed5ad944a62faf93dc425e2

Includes the new "pcie-max-link-speed" NVRAM parameter, and modifies the
phb4 default speed for POWER9 DD1.

Signed-off-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>
diff --git a/openpower/configs/zz_defconfig b/openpower/configs/zz_defconfig
index bcbe33a..ddc3504 100644
--- a/openpower/configs/zz_defconfig
+++ b/openpower/configs/zz_defconfig
@@ -51,7 +51,7 @@
 # BR2_PACKAGE_OCC is not set
 # BR2_PACKAGE_CAPP_UCODE is not set
 BR2_SKIBOOT_CUSTOM_VERSION=y
-BR2_SKIBOOT_CUSTOM_VERSION_VALUE="6a3a09c27315d858647a1c978fa7032591a8e6c5"
+BR2_SKIBOOT_CUSTOM_VERSION_VALUE="950577e5dddeb99c1ed5ad944a62faf93dc425e2"
 BR2_PACKAGE_LOADKEYS=y
 # BR2_PACKAGE_HOST_PPE42_BINUTILS is not set
 # BR2_PACKAGE_HOST_PPE42_GCC is not set