doc: merge Linux requirements for applications build

doc: merge Linux requirements for applications build

When building end-applications linked with DPDK, the only additional
tool needed is pkg-config/pkgconf. However, the standard development
tools meta-packages on most distro's include this as standard, meaning
it does not really require its own section. The one outlier in the
existing text is "alpine" where it is not present when using "libc-dev"
target. However, changing "gcc" and "libc-dev" to "alpine-sdk"
metapackage aligns alpine with the other distros in this regard.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>