i2c: Update references to individual i2c commands

The individual i2c commands imd, imm, inm, imw, icrc32, iprobe, iloop,
and isdram are no longer available so all references to them have been
updated to the new form of "i2c <cmd>".

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>
diff --git a/doc/README.m54455evb b/doc/README.m54455evb
index f695da5..b769ff9 100644
--- a/doc/README.m54455evb
+++ b/doc/README.m54455evb
@@ -304,17 +304,11 @@
 fsload	- load binary file from a filesystem image
 go      - start application at address 'addr'
 help    - print online help
+i2c     - I2C sub-system
 icache  - enable or disable instruction cache
-icrc32  - checksum calculation
 ide     - IDE sub-system
-iloop   - infinite loop on address range
-imd     - i2c memory display
 iminfo  - print header information for application image
 imls    - list all images found in flash
-imm     - i2c memory modify (auto-incrementing)
-imw     - memory write (fill)
-inm     - memory modify (constant address)
-iprobe  - probe to discover valid I2C chip addresses
 itest	- return true/false on integer compare
 loadb   - load binary file over serial line (kermit mode)
 loads   - load S-Record file over serial line