meta-ibm: p10bmc: Set FLASH_SIZE to exclude u-boot configurations

Explicitly set FLASH_SIZE to prevent SPI-flash related configurations
being pulled into the build. Specifically this prevents the default
value provided by meta-phosphor triggering the uboot-flash-32768
override. The override pulls the u-boot_flash_32M.cfg configuration into
the build, breaking the environment handling for p10bmc machines which
exclusively use eMMC.

Change-Id: Ice0e2be27d5bd7ca207dcaf91ea311137fc55439
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/meta-ibm/conf/machine/p10bmc.conf b/meta-ibm/conf/machine/p10bmc.conf
index a0ad416..6a6258f 100644
--- a/meta-ibm/conf/machine/p10bmc.conf
+++ b/meta-ibm/conf/machine/p10bmc.conf
@@ -80,3 +80,5 @@
 QB_FSINFO = "wic:no-kernel-in-fs"
 QB_DEFAULT_KERNEL:p10bmc="zImage"
 QB_KERNEL_ROOT:p10bmc="PARTLABEL=rofs-a"
+
+FLASH_SIZE = "16777216"