lm3s: add LM3S811 eval board miniblink example

The LM3S811-EVB miniblink example is a copy of the LM3S3748-EVB miniblink
example.  Modifications:

 - rename lm3s3748-evb.ld to lm3s811-evb.ld and change RAM and ROM sizes
 - amend Makefile to reference the lm3s811-evb.ld linker script
 - amend miniblink.c to use PC5 instead of PF0 for the LED GPIO
 - amend README to reference LM3S811-EVB instead of LM3S3748-EVB