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/socfpga_stratix10_atf_defconfig b/configs/socfpga_stratix10_atf_defconfig
index 50bab70..db48695 100644
--- a/configs/socfpga_stratix10_atf_defconfig
+++ b/configs/socfpga_stratix10_atf_defconfig
@@ -33,6 +33,7 @@
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="SOCFPGA_STRATIX10 # "
 CONFIG_SYS_MAXARGS=64
+CONFIG_SYS_PBSIZE=2085
 CONFIG_CMD_MEMTEST=y
 # CONFIG_CMD_FLASH is not set
 CONFIG_CMD_GPIO=y