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/pcm052_defconfig b/configs/pcm052_defconfig
index 264bff8..a9580be 100644
--- a/configs/pcm052_defconfig
+++ b/configs/pcm052_defconfig
@@ -22,6 +22,7 @@
 CONFIG_BOOTCOMMAND="run bootcmd_nand"
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_HUSH_PARSER=y
+CONFIG_SYS_PBSIZE=276
 CONFIG_CMD_BOOTZ=y
 CONFIG_CMD_MEMTEST=y
 CONFIG_CMD_GPIO=y