lib: add crc16.o if CONFIG_MMC_SPI_CRC_ON for SPL build

CONFIG_MMC_SPI_CRC_ON needs the crc16 functions, but it was not included
in an SPL build.  For non-SPL builds, crc16.o is already added
unconditionally.  This also removes CONFIG_SPL_YMODEM_SUPPORT from the
sifive board configs, which is only relevant for some ARM boards and was
only set for its side effect of adding crc16.o.
diff --git a/configs/sifive_unleashed_defconfig b/configs/sifive_unleashed_defconfig
index cf50101..be947be 100644
--- a/configs/sifive_unleashed_defconfig
+++ b/configs/sifive_unleashed_defconfig
@@ -24,7 +24,6 @@
 CONFIG_SPL_DM_SPI_FLASH=y
 CONFIG_SPL_DM_RESET=y
 CONFIG_SPL_SPI_LOAD=y
-CONFIG_SPL_YMODEM_SUPPORT=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_SPL_DM_SEQ_ALIAS=y
 CONFIG_SPL_CLK=y
diff --git a/configs/sifive_unmatched_defconfig b/configs/sifive_unmatched_defconfig
index 890d3a0..3d478ad 100644
--- a/configs/sifive_unmatched_defconfig
+++ b/configs/sifive_unmatched_defconfig
@@ -23,7 +23,6 @@
 CONFIG_ID_EEPROM=y
 CONFIG_SPL_SEPARATE_BSS=y
 CONFIG_SPL_DM_RESET=y
-CONFIG_SPL_YMODEM_SUPPORT=y
 CONFIG_CMD_EEPROM=y
 CONFIG_CMD_MEMINFO=y
 CONFIG_CMD_PWM=y
diff --git a/lib/Makefile b/lib/Makefile
index 8ba745f..2d29cda 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -88,6 +88,7 @@
 ifdef CONFIG_SPL_BUILD
 obj-$(CONFIG_SPL_YMODEM_SUPPORT) += crc16.o
 obj-$(CONFIG_$(SPL_TPL_)HASH_SUPPORT) += crc16.o
+obj-$(CONFIG_MMC_SPI_CRC_ON) += crc16.o
 obj-y += net_utils.o
 endif
 obj-$(CONFIG_ADDR_MAP) += addr_map.o