arm: lpc32xx: add CONFIG_ARCH_LPC32XX build option

The explicit arch specific build symbol allows to group supported
boards, generalize common config options and it will serve as
a dependency for platform only drivers.

Two related board defconfigs are resynced after the change.

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
diff --git a/configs/work_92105_defconfig b/configs/work_92105_defconfig
index 7504077..105e51a 100644
--- a/configs/work_92105_defconfig
+++ b/configs/work_92105_defconfig
@@ -1,12 +1,13 @@
 CONFIG_ARM=y
-CONFIG_TARGET_WORK_92105=y
+CONFIG_ARCH_LPC32XX=y
 CONFIG_SYS_TEXT_BASE=0x80100000
 CONFIG_SPL_LIBCOMMON_SUPPORT=y
 CONFIG_SPL_LIBGENERIC_SUPPORT=y
-CONFIG_SPL_SERIAL_SUPPORT=y
-CONFIG_SPL=y
+CONFIG_TARGET_WORK_92105=y
 CONFIG_CMD_HD44760=y
 CONFIG_CMD_MAX6957=y
+CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL=y
 CONFIG_NR_DRAM_BANKS=2
 CONFIG_BOOTDELAY=3
 CONFIG_USE_BOOTARGS=y
@@ -32,13 +33,9 @@
 CONFIG_CMD_DATE=y
 CONFIG_DOS_PARTITION=y
 CONFIG_ENV_IS_IN_NAND=y
-CONFIG_DM=y
-CONFIG_SPL_DM=y
-CONFIG_DM_GPIO=y
 # CONFIG_MMC is not set
 CONFIG_PHYLIB=y
 CONFIG_PHY_ADDR_ENABLE=y
-CONFIG_DM_SERIAL=y
 CONFIG_SYS_NS16550=y
 CONFIG_SPI=y
 CONFIG_LPC32XX_SSP=y