Convert CONFIG_SYS_PBSIZE to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_PBSIZE

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/trimslice_defconfig b/configs/trimslice_defconfig
index a435fe1..03e6e7c 100644
--- a/configs/trimslice_defconfig
+++ b/configs/trimslice_defconfig
@@ -16,6 +16,7 @@
 CONFIG_SYS_STDIO_DEREGISTER=y
 CONFIG_SYS_PROMPT="Tegra20 (TrimSlice) # "
 CONFIG_SYS_MAXARGS=64
+CONFIG_SYS_PBSIZE=2087
 # CONFIG_CMD_IMI is not set
 CONFIG_CMD_GPIO=y
 CONFIG_CMD_I2C=y