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/omap3_evm_defconfig b/configs/omap3_evm_defconfig
index b7fd976..a4bcb43 100644
--- a/configs/omap3_evm_defconfig
+++ b/configs/omap3_evm_defconfig
@@ -23,6 +23,7 @@
 CONFIG_SPL_NAND_BASE=y
 CONFIG_SYS_PROMPT="OMAP3_EVM # "
 CONFIG_SYS_MAXARGS=64
+CONFIG_SYS_PBSIZE=1053
 CONFIG_CMD_SPL=y
 CONFIG_CMD_SPL_NAND_OFS=0x280000
 CONFIG_CMD_SPL_WRITE_SIZE=0x20000