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/chromebook_link64_defconfig b/configs/chromebook_link64_defconfig
index b29c5cc..46397c3 100644
--- a/configs/chromebook_link64_defconfig
+++ b/configs/chromebook_link64_defconfig
@@ -42,6 +42,7 @@
 CONFIG_SPL_PCH=y
 CONFIG_SPL_RTC=y
 CONFIG_HUSH_PARSER=y
+CONFIG_SYS_PBSIZE=532
 CONFIG_CMD_CPU=y
 CONFIG_CMD_GPIO=y
 CONFIG_CMD_SPI=y