mpc83xx: Get rid of CONFIG_83XX_CLKIN

MPC83xx uses CONFIG_83XX_CLKIN instead of CONFIG_SYS_CLK_FREQ to set the
system clock. To migrate the architecture, we can replace
CONFIG_83XX_CLKIN with CONFIG_SYS_CLK_FREQ.

To do this
* replace all occurrences of CONFIG_83XX_CLKIN with CONFIG_SYS_CLK_FREQ
* set CONFIG_SYS_CLK_FREQ to the old value of CONFIG_83XX_CLKIN in all
  MPC83xx config files

Signed-off-by: Mario Six <mario.six@gdsys.cc>
diff --git a/configs/MPC8313ERDB_NAND_33_defconfig b/configs/MPC8313ERDB_NAND_33_defconfig
index bcb83b1..80ed52b 100644
--- a/configs/MPC8313ERDB_NAND_33_defconfig
+++ b/configs/MPC8313ERDB_NAND_33_defconfig
@@ -2,6 +2,7 @@
 CONFIG_SYS_TEXT_BASE=0x00100000
 CONFIG_SPL_SERIAL_SUPPORT=y
 CONFIG_SPL=y
+CONFIG_SYS_CLK_FREQ=33333333
 CONFIG_MPC83xx=y
 CONFIG_TARGET_MPC8313ERDB_NAND=y
 CONFIG_OF_BOARD_SETUP=y