[console] Allow '?' as an intermediate byte in ANSI escape sequences

The ANSI escape sequences to show and hide the cursor take the form
"<ESC>[?25h" and "<ESC>[?25l" respectively.  iPXE currently treats the
'?' character as the final byte.  Fix by explicitly treating '?' as an
intermediate byte.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/ansiesc.c

 				DBG ( "Too many parameters in ANSI escape "
 				      "sequence\n" );
 			}
-		} else if ( ( c >= 0x20 ) && ( c <= 0x2f ) ) {
+		} else if ( ( ( c >= 0x20 ) && ( c <= 0x2f ) ) ||
+			    ( c == '?' ) ) {
 			/* Intermediate Byte */
 			ctx->function <<= 8;
 			ctx->function |= c;

src/include/ipxe/ansiesc.h

  */
 #define ANSIESC_LOG_PRIORITY 'p'
 
+/** Show cursor */
+#define ANSIESC_DECTCEM_SET ( ( '?' << 8 ) | 'h' )
+
+/** Hide cursor */
+#define ANSIESC_DECTCEM_RESET ( ( '?' << 8 ) | 'l' )
+
 /** @} */
 
 extern int ansiesc_process ( struct ansiesc_context *ctx, int c );