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/mt7623n_bpir2_defconfig b/configs/mt7623n_bpir2_defconfig
index e2d68b9..b65b597 100644
--- a/configs/mt7623n_bpir2_defconfig
+++ b/configs/mt7623n_bpir2_defconfig
@@ -18,6 +18,7 @@
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_SYS_PROMPT="U-Boot> "
 CONFIG_SYS_MAXARGS=8
+CONFIG_SYS_PBSIZE=1049
 CONFIG_CMD_BOOTMENU=y
 # CONFIG_CMD_ELF is not set
 # CONFIG_CMD_XIMG is not set