m68k: Drop unreferenced CONFIG_* defines

The following config symbols are only defined once and never referenced
anywhere else:

CONFIG_AMCORE
CONFIG_ASTRO5373L
CONFIG_M52277EVB
CONFIG_M5253DEMO
CONFIG_M5253EVBE
CONFIG_M5275EVB
CONFIG_M54418TWR
CONFIG_STMARK2

Most of them are config symbols named after the respective boards which
seems to have been a standard practice at some point.

Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>

scripts/config_whitelist.txt

@@ -29,7 +29,6 @@ CONFIG_AM335X_USB0_MODE
 CONFIG_AM335X_USB1
 CONFIG_AM335X_USB1_MODE
 CONFIG_AM437X_USB2PHY2_HOST
-CONFIG_AMCORE
 CONFIG_ANDES_PCU
 CONFIG_ANDES_PCU_BASE
 CONFIG_APBH_DMA
@@ -72,7 +71,6 @@ CONFIG_ARM_PL180_MMCI_BASE
 CONFIG_ARM_PL180_MMCI_CLOCK_FREQ
 CONFIG_ARM_THUMB
 CONFIG_ARP_TIMEOUT
-CONFIG_ASTRO5373L
 CONFIG_ASTRO_COFDMDUOS2
 CONFIG_ASTRO_TWIN7S2
 CONFIG_ASTRO_V512
@@ -1275,12 +1273,7 @@ CONFIG_LSXHL
 CONFIG_LYNXKDI
 CONFIG_M41T94_SPI_CS
 CONFIG_M520x
-CONFIG_M52277EVB
-CONFIG_M5253DEMO
-CONFIG_M5253EVBE
-CONFIG_M5275EVB
 CONFIG_M5301x
-CONFIG_M54418TWR
 CONFIG_M54451EVB
 CONFIG_M54455EVB
 CONFIG_MACB0_PHY
@@ -2165,7 +2158,6 @@ CONFIG_STM32_GPIO
 CONFIG_STM32_HSE_HZ
 CONFIG_STM32_HZ
 CONFIG_STM32_SERIAL
-CONFIG_STMARK2
 CONFIG_STRIDER
 CONFIG_STRIDER_CON
 CONFIG_STRIDER_CON_DP