NuttX defconfig minor cleanup and improvements

[dagar]

• remove all the unnecessary entries disabling NXFONTS
• don't exclude procfs entries (enables df and a few other things)
• enable tab completion and command line history on newer boards with plenty of memory (f7, h7, imxrt)

Example: df

nsh> df -h
  Filesystem    Size      Used  Available Mounted on
  cromfs        204K      204K         0B /etc
  vfat           14G       95M        14G /fs/microsd
  procfs          0B        0B         0B /proc

Example: tab completion (a tab)

nsh> a
  adc
  adis16448
  ak09916
  adis16477
  adis16497
  attitude_estimator_q
  airspeed_selector
nsh> a

TODO: review possible mavlink nsh issues

@davids5 I vaguely recall you encountered an issue with either tab completion or command line history with nsh over mavlink. What was the problem?

[dagar]

Rebased with the tab completion and history removed (we can try again later).