fs: add filesystem switch libary, implement ls and fsload commands

Implement "ls" and "fsload" commands that act like {fat,ext2}{ls,load},
and transparently handle either file-system. This scheme could easily be
extended to other filesystem types; I only didn't do it for zfs because
I don't have any filesystems of that type to test with.

Replace the implementation of {fat,ext[24]}{ls,load} with this new code
too.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
diff --git a/common/Makefile b/common/Makefile
index eac6360..9e43322 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -90,11 +90,6 @@
 COBJS-$(CONFIG_SYS_HUSH_PARSER) += cmd_exit.o
 COBJS-$(CONFIG_CMD_EXT4) += cmd_ext4.o
 COBJS-$(CONFIG_CMD_EXT2) += cmd_ext2.o
-ifdef CONFIG_CMD_EXT4
-COBJS-y	+= cmd_ext_common.o
-else
-COBJS-$(CONFIG_CMD_EXT2) += cmd_ext_common.o
-endif
 COBJS-$(CONFIG_CMD_FAT) += cmd_fat.o
 COBJS-$(CONFIG_CMD_FDC)$(CONFIG_CMD_FDOS) += cmd_fdc.o
 COBJS-$(CONFIG_OF_LIBFDT) += cmd_fdt.o fdt_support.o
@@ -104,6 +99,7 @@
 ifdef CONFIG_FPGA
 COBJS-$(CONFIG_CMD_FPGA) += cmd_fpga.o
 endif
+COBJS-$(CONFIG_CMD_FS_GENERIC) += cmd_fs.o
 COBJS-$(CONFIG_CMD_GPIO) += cmd_gpio.o
 COBJS-$(CONFIG_CMD_I2C) += cmd_i2c.o
 COBJS-$(CONFIG_CMD_IDE) += cmd_ide.o