Now that we have an SDHCI driver, enable the block layer, and common
filesystems; MSDOS/VFAT for the SoC-required firmware partition, ext2/3/4
for a root partition.

Add tmpfs, NFS, file locking, file notify, networking, and NLS to support
distro expectations.

Enable GPIO_SYSFS to allow GPIO twiddling from user-space; likely a
common activity on this hardware.

Enable I2C.

Remove bogus CONFIG_DEFAULT_MMAP_MIN_ADDR so that applications running as
non-root actually work; without this, execve() immediately triggers
SIGKILL. This setting was sourced from some downstream defconfig early
during upstream Raspberry Pi support development.

Other non-semantic diffs due to rebuilding defconfig using the latest
Kconfig defaults etc.
Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>