powerpc: mpc8536ds: Enable DHCP command by default

Enable DHCP command to make TFTP easier. Users don't have to use
static IP address.

Signed-off-by: York Sun <york.sun@nxp.com>

configs/MPC8536DS_36BIT_defconfig

@@ -10,6 +10,7 @@ CONFIG_BOOTDELAY=10
 # CONFIG_CONSOLE_MUX is not set
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_HUSH_PARSER=y
+CONFIG_CMD_DHCP=y
 CONFIG_CMD_MMC=y
 CONFIG_CMD_SF=y
 CONFIG_CMD_I2C=y

configs/MPC8536DS_defconfig

@@ -9,6 +9,7 @@ CONFIG_BOOTDELAY=10
 # CONFIG_CONSOLE_MUX is not set
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_HUSH_PARSER=y
+CONFIG_CMD_DHCP=y
 CONFIG_CMD_MMC=y
 CONFIG_CMD_SF=y
 CONFIG_CMD_I2C=y