[ARM] 4737/1: Refactor corgi_lcd to improve readability + bugfix

This patch refactors the code in corgi_lcd.c moving it to the board
specific corgi and spitz files where appropriate instead of the
existing ifdef mess which hinders readability.

Fix spitz_get_hsync_len() to call get_hsync_invperiod so pxafb can be
compiled as a module.

The confusing variables which represent the inverse horizintal sync
period are renamed to "invperiod" consistently.

An incorrect comment in corgi_ts.c is also corrected.

Signed-off-by: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>