sh: update r2d defconfig and fix SH7751R pci compliation

This patch updates the r2d board support in a few ways:

- CPU_SUBTYPE_SH7751R is selected in the defconfig to play well
  with the r2d board Kconfig entry. Without this the defconfig
  results in no board enabled.

- Enable EARLY_PRINTK.
- Enable SH_STANDARD_BIOS
	- this works well for early printk on the r2d board.

- Add "earlyprink=bios" to the cmdline for early serial port
  output by default.

- CONFIG_SUBTYPE_SH7751R support is added to the sh-specific
  pci makefile.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>